Light emitting device and method of manufacturing the same

ABSTRACT

The present invention has an object of providing a light emitting device including an OLED formed on a plastic substrate, which can prevent the degradation due to penetration of moisture or oxygen. On a plastic substrate, a plurality of films for preventing oxygen or moisture from penetrating into an organic light emitting layer in the OLED (hereinafter, referred to as barrier films) and a film having a smaller stress than that of the barrier films (hereinafter, referred to as a stress relaxing film), the film being interposed between the barrier films, are provided. Owing to a laminate structure of a plurality of barrier films, even if a crack occurs in one of the barrier films, the other barrier film(s) can effectively prevent moisture or oxygen from penetrating into the organic light emitting layer. Moreover, the stress relaxing film, which has a smaller stress than that of the barrier films, is interposed between the barrier films, thereby making it possible to reduce a stress of the entire sealing film. As a result, a crack due to stress hardly occurs.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of manufacturing asemiconductor device, more specifically, to a light emitting deviceincluding a light emitting element, for example, an organic lightemitting diode (OLED), formed on a plastic substrate. The presentinvention also relates to an OLED module in which an IC including acontroller and the like is mounted onto an OLED panel. Throughout thespecification, OLED panels and OLED modules are generically referred toas light emitting devices. The present invention further relates to anelectrical appliance using the light emitting device.

2. Description of the Related Art

Recently, a technique for forming a TFT (thin film transistor) on asubstrate has been remarkably developed, and continues to be furtherdeveloped for its application to active matrix display devices.Particularly, a TFT using a polysilicon film can operate at a high speedbecause such a TFT has a higher field effect mobility than a TFT using aconventional amorphous silicon film. Therefore, the control of pixels,which has been conventionally performed by a driver circuit providedoutside a substrate, can be now performed by a driver circuit providedon the same substrate on which the pixels are formed.

Such an active matrix display device includes various circuits orelements formed on the same substrate. Owing to this structure, theactive matrix display device provides various advantages such as reducedmanufacturing cost, reduced size of a display device, an increasedyield, and an increased throughput.

Furthermore, an active matrix light emitting device including an OLED asa self-luminous element (hereinafter, simply referred to as a lightemitting device) has been actively studied. The light emitting device isalso called an organic EL display (OELD) or an organic light emittingdiode.

The OLED is optimal for reduction in thickness of a light emittingdevice because it has a high visibility for its self-luminescence andthus it does not require a backlight which is necessary for a liquidcrystal display (LCD). Moreover, the OLED is further advantageous in itsunlimited viewing angle. For these advantages, light emitting devicesusing the OLED attract attention as display devices replacing CRTs orLCDs.

The OLED includes a layer containing an organic compound (organic lightemitting material; such a layer is referred to as an organic lightemitting layer, hereinafter), an anode layer and a cathode layer. Theorganic light emitting layer generates luminescence(electroluminescence) by applying an electric field across the anode andthe cathode. The electroluminescence generated from the organic compoundincludes: light emission (fluorescence) caused upon return from asinglet excited state to a ground state; and light emission(phosphorescence) caused upon return from a triplet excited state to aground state. The light emitting device of the present invention may useeither one of the above-described types of light emission;alternatively, it may use both types of light emission.

In this specification, all layers provided between a cathode and ananode of an OLED are generically defined as organic light emittinglayers. Specifically, a light emitting layer, a hole injection layer, anelectron injection layer, a hole transporting layer, an electrontransporting layer and the like are all included in the category oforganic light emitting layers. The OLED basically has a structure inwhich an anode, a light emitting layer and a cathode are layered in thisorder. In addition to this structure, some OLEDs have a structureincluding an anode, a hole injection layer, a light emitting layer and acathode layered in this order, and other OLEDs have a structureincluding an anode, a hole injection layer, a light emitting layer, anelectron transporting layer, a cathode and the like layered in thisorder.

Such a light emitting device is expected to be used for variousapplications. In particular, the light emitting device is desired to beapplied to portable equipment for its small thickness and thus thepossibility of reduction in weight. For this propose, an attempt hasbeen made to form an OLED on a flexible plastic film.

A light emitting device, in which an OLED is formed on a flexiblesubstrate such as a plastic film, is advantageous not only in its smallthickness and light weight but also its utility for a display having acurved surface, a show window and the like. Therefore, its applicationrange is extremely wide, not limited to portable equipment.

However, a substrate made of plastic is generally likely to allowmoisture or oxygen to pass through. Since the degradation of an organiclight emitting layer is accelerated by moisture and oxygen, the lifetimeof a light emitting device tends to be short by the penetration ofmoisture or oxygen. As a conventional solution of this problem, aninsulating film such as a silicon nitride film or a silicon oxynitridefilm is provided between the plastic substrate and the OLED so as toprevent moisture or oxygen from penetrating into the organic lightemitting layer.

In general, however, a substrate such as a plastic film is easilyaffected by heat. At an excessively elevated film formation temperaturefor an insulating film such as a silicon nitride film or a siliconoxynitride film, a substrate is likely to be deformed. On the contrary,at an excessively low film formation temperature, the quality of a filmmay be degraded, making it difficult to sufficiently prevent thepenetration of moisture or oxygen.

Furthermore, if a thickness of an insulating film such as a siliconnitride film or a silicon oxynitride film is increased so as to preventthe penetration of moisture or oxygen, a stress is correspondinglyincreased to easily cause a crack in the film. Moreover, with anincrease in thickness, a crack is likely to be generated in theinsulating film when the substrate is bent.

SUMMARY OF THE INVENTION

In view of the above problems, the present invention has an object ofproviding a light emitting device including an OLED formed on a plasticsubstrate, which is capable of restraining the degradation due topenetration of moisture or oxygen.

According to the present invention, a plurality of films which preventoxygen or moisture from penetrating into an organic light emitting layerof an OLED (hereinafter, referred to as barrier films) and a layerhaving a smaller stress than that of the barrier films (hereinafter,referred to as a stress relaxing film), being sandwiched between thebarrier films, are provided on a plastic substrate. Throughout thespecification, a film formed by a laminate of the barrier films and thestress relaxing film is referred to as a sealing film.

Specifically, two or more barrier films made of an inorganic material(hereinafter, simply referred to as barrier films) are provided.Furthermore, a stress relaxing film containing a resin (hereinafter,simply referred to as a stress relaxing film) is provided between thebarrier films. Then, an OLED is formed on these three or more layers ofthe insulating films. The OLED is sealed to complete a light emittingdevice.

According to the present invention, a plurality of barrier films arelaminated. In this manner, even if a crack occurs in one of the barrierfilms, the other barrier film(s) can effectively prevent moisture oroxygen from penetrating into the organic light emitting layer. Moreover,even though the quality of barrier films is degraded due to a low filmformation temperature, a laminate of a plurality of barrier films caneffectively prevent moisture or oxygen from penetrating into the organiclight emitting layer.

Furthermore, a stress relaxing film, which has a smaller stress thanthat of the barrier film, is sandwiched between the barrier films toreduce the entire stress of the sealing film. Thus, a crack due tostress hardly occurs in a multi-layered barrier film, in which a stressrelaxing film is interposed between barrier films, as compared with asingle-layered barrier film having the same thickness.

Accordingly, a multi-layered barrier film can effectively preventmoisture or oxygen from penetrating into the organic light emittinglayer as compared with a single-layered barrier film having the samethickness. In addition, a crack due to stress hardly occurs in such amulti-layered barrier film.

Moreover, a laminate structure of barrier films and a stress relaxingfilm provides a further flexibility to a device, thereby preventing acrack upon bend of the substrate.

Furthermore, according to the present invention, a film for sealing fanOLED formed on a substrate (hereinafter, referred to as a sealing film)may also have the above-mentioned multi-layered structure. With such astructure, moisture or oxygen can be effectively prevented frompenetrating into the organic light emitting layer. In addition, a crackis prevented from occurring upon bend of the substrate. As a result, alight emitting device having enhanced flexibility can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1C are diagrams showing the manufacturing methods of a lightemitting device according to the present invention;

FIGS. 2A and 2B are diagrams showing the manufacturing methods of thelight emitting device according to the present invention;

FIGS. 3A to 3D are diagrams showing the manufacturing methods of thelight emitting device according to the present invention;

FIGS. 4A to 4C are diagrams showing the manufacturing methods of thelight emitting device according to the present invention;

FIG. 5A is a diagram showing the appearance of a light emitting deviceaccording to the present invention; FIG. 5B is an enlarged view showinga connecting portion with an FPC; and FIG. 5C is a cross-sectional viewshowing the connecting portion;

FIG. 6A is a diagram showing a light emitting device according to thepresent invention in a bent state; and FIG. 6B is a cross-sectional viewthereof;

FIG. 7 is a cross-sectional view showing a portion where a lightemitting device according to the present invention is connected with anFPC;

FIGS. 8A to 8D are diagrams showing the manufacturing methods of a lightemitting device according to the present invention;

FIGS. 9A to 9C are diagrams showing the manufacturing methods of thelight emitting device according to the present invention;

FIGS. 10A to 10C are diagrams showing the steps of manufacturing a TFTand an OLED included in a light emitting device according to the presentinvention;

FIGS. 11A to 11C are diagrams showing the steps of manufacturing a TFTand an OLED included in the light emitting device according to thepresent invention;

FIGS. 12A and 12B are diagrams showing the steps of manufacturing a TFTand an OLED included in the light emitting device according to thepresent invention;

FIG. 13 is a cross-sectional view showing a light emitting, deviceaccording to the present invention;

FIG. 14 is a diagram showing removal of a bonding layer by a water jetmethod;

FIG. 15 is a diagram showing formation of an organic light emittinglayer by spraying;

FIG. 16A is a top view showing a pixel, and FIG. 16B is a circuitdiagram of a pixel;

FIG. 17 is a schematic diagram showing a circuit structure of a lightemitting device;

FIGS. 18A to 18D are diagrams, each showing an electronic applianceusing a light emitting device according to the present invention; and

FIG. 19 is a diagram showing a sealing film formation apparatusemploying a roll-to-roll method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiment modes of the present invention will be describedwith reference to the accompanying drawings. FIGS. 1A through 4C arecross-sectional views showing the manufacturing steps in a pixel portionand a driving circuit.

Embodiment Mode 1

In FIG. 1A, a first bonding layer 102 made of an amorphous silicon filmis formed to have a thickness of 100 to 500 nm (300 nm in thisembodiment mode) on a first substrate 101. Although a glass substrate isused as the first substrate 101 in this embodiment mode, a quartzsubstrate, a silicon substrate, a metal substrate or a ceramic substratemay be alternatively used. Any material can be used for the firstsubstrate 101 as long as it is resistant to a treatment temperature inthe later manufacturing steps.

As a method of forming the first bonding layer 102, a low pressurethermal CVD method, a plasma CVD method, a sputtering method or anevaporation method may be used. On the first bonding layer 102, aninsulating film 103 made of a silicon oxide film is formed to have athickness of 200 nm. As a method of forming the insulating film 103, alow pressure thermal CVD method, a plasma CVD method, a sputteringmethod or an evaporation method may be used. The insulating film 103serves to protect an element formed on the first substrate 101 when thefirst bonding layer 102 is removed to peel off the first substrate 101.

Next, an element is formed on the insulating film 103 (FIG. 1B). Theelement herein designates a semiconductor element (typically, a TFT) oran MIM element, which is used as a switching element for a pixel, anOLED and the like in the case of an active matrix light emitting device.In the case of a passive light emitting device, the element designatesan OLED. In FIG. 1B, a TFT 104 a in a driving circuit 106, TFTs 104 band 104 c and an OLED 105 in a pixel portion are shown as representativeelements.

Then, an insulating film 108 is formed so as to cover theabove-described elements. It is preferred that the insulating film 108has a flatter surface after its formation. It is not necessarilyrequired to provide the insulating film 108.

Next, as shown in FIG. 1C, a second substrate 110 is bonded to the firstsubstrate 101 through a second bonding layer 109. In this embodimentmode, a plastic substrate is used as the second substrate 110. Morespecifically, a resin substrate having a thickness of is 10 μm or more,for example, a substrate made of PES (polyether sulfone), PC(polycarbonate), PET (polyethylene terephthalate) or PEN (polyethylenenaphthalate) can be used.

As a material of the second bonding layer 109, it is necessary to usesuch a material that can provide a high selection ratio when the firstbonding layer 102 is to be removed in the later step. Typically, aninsulating film made of a resin can be used as the second bonding layer109. Although polyimide is used as a material of the second bondinglayer 109 in this embodiment mode, acryl, polyamide or an epoxy resincan be alternatively used. In the case where the second bonding layer109 is placed on the viewer side (the side of a light emitting deviceuser) when seen from the OLED, a material is required to have lighttransmittance.

Furthermore, in this embodiment mode, two or more barrier films areformed on the second substrate 110. Then, a stress relaxing film isprovided between the two barrier films. As a result, a sealing filmhaving a laminate structure of the barrier films and the stress relaxingfilm is formed between the second substrate 110 and the second bondinglayer 109.

For example, in this embodiment mode, a film made of silicon nitride isformed as a barrier film 111 a by sputtering on the second substrate110; a stress relaxing film 111 b containing polyimide is formed on thebarrier film 111 a; and a film made of silicon nitride is formed as abarrier film 111 c by sputtering on the stress relaxing film 111 b. Alaminate film of the barrier film 111 a, the stress relaxing film 111 band the barrier film 111 c is collectively referred to as a sealing film111. Then, the second substrate 110, on which the sealing film 111 isformed, is bonded to the element formed on the first substrate 101through the second bonding layer 109.

It is sufficient to provide two or more barrier films. As a material ofthe barrier films, silicon nitride, silicon oxynitride, aluminum oxide,aluminum nitride, aluminum oxynitride or aluminum silicide oxynitride(AlSiON) can be used.

Since aluminum silicide oxynitride has a relatively high thermalconductivity, its use for the barrier films allows efficient radiationof heat that is generated in the element.

A resin having light transmittance can be used for the stress relaxingfilm 111 b. Typically, polyimide, acryl, polyamide, polyimide amide,benzocyclobutene, an epoxy resin or the like can be used. Resins otherthan the above-described resins can also be used. In this embodimentmode, the stress relaxing film is formed by application of thermallypolymerizable polyimide, followed by baking.

A silicon nitride film is formed by introducing argon at a substratetemperature kept at 150° C. under a sputtering pressure of about 0.4 Pa.Film formation is conducted using silicon as a target with introductionof nitrogen and hydrogen in addition to argon. In the case of siliconoxynitride, a film is formed by introducing argon at a substratetemperature kept at 150° C. under a sputtering pressure of about 0.4 Pa.Film formation is conducted using silicon as a target while introducingnitrogen, nitrogen dioxide and hydrogen in addition to argon. Siliconoxide may be alternatively used as a target.

It is desirable that each of the barrier films 111 a and 111 c has athickness in the range of 50 nm to 3 μm. In this embodiment mode, asilicon nitride film is formed to have a thickness of 1 μm.

A method of forming the barrier films is not limited to sputtering; afilm formation method can be suitably determined by those who carry outthe invention. For example, the barrier films may be formed by an LPCVDmethod, a plasma CVD method or the like.

It is desirable that the stress relaxing film 111 b has a thickness inthe range of 200 nm to 2 μm. In this embodiment mode, a polyimide filmis formed to have a thickness of 1 μm as the stress relaxing film.

For the barrier films 111 a and 111 c and the stress relaxing film 111b, it is required to use materials which provide a high selection ratiowhen the first bonding layer 102 is to be removed in the later step.

Owing to the step shown in FIG. 1A, the OLED can be completely isolatedfrom air. As a result, the degradation of the organic light emittingmaterial due to oxidation can be substantially completely restrained,thereby remarkably improving the reliability of the OLED.

Next, as shown in FIG. 2A, the first substrate 101, the second substrate110 and all the elements and the entire films formed therebetween areexposed to a gas containing halogen fluoride so as to remove the firstbonding layer 102. In this embodiment mode, chlorine trifluoride (ClF₃)is used as halogen fluoride, and nitrogen is used as a diluent gas.Alternatively, argon, helium or neon may be used as a diluent gas. Aflow rate may be set to 500 sccm (8.35×10⁻⁶ m³/s) for both gases, and areaction pressure may be set to 1 to 10 Torr (1.3×10² to 1.3×10³ Pa). Atreatment temperature may be a room temperature (typically, 20 to 27°C.).

In this case, the silicon film is etched whereas the plastic film, theglass substrate, the polyimide film, and the silicon oxide film are notetched. More specifically, through exposure to chlorine trifluoride, thefirst bonding layer 102 is selectively etched to result in completeremoval thereof. Since an active layer of the TFT, which is similarlymade of a silicon layer, is not exposed to the outside, the active layeris not exposed to chlorine trifluoride and therefore is not etched.

In this embodiment mode, the first bonding layer 102 is gradually etchedfrom its exposed edge portions. The first substrate 101 and theinsulating film 103 are separated from each other when the first bondinglayer 102 is completely removed. The TFTs and the OLED, each of whichincludes a laminate of thin films, remain on the second substrate 110.

A large-sized substrate is not preferred as the first substrate 101because the etching gradually proceeds from the edges of the firstbonding layer 102 and therefore the time required for completelyremoving the first bonding layer 102 gets long with increase in size.Therefore, it is desirable that this embodiment mode is carried out forthe first substrate 101 having a diagonal of 3 inches or less(preferably, 1 inch or less).

After the peeling of the first substrate 101 in this manner, a thirdbonding layer 113 is formed as shown in FIG. 2B. Then, a third substrate112 is bonded to the second substrate 110 through the third bondinglayer 113. In this embodiment mode, a plastic substrate is used as thethird substrate 112. More specifically, a resin substrate having athickness of 10 μm or more, for example, a substrate made of PES(polyether sulfone), PC (polycarbonate), PET (polyethyleneterephthalate) or PEN (polyethylene naphthalate) can be used as thethird substrate 112.

As the third bonding layer 113, an insulating film made of a resin(typically, polyimide, acryl, polyamide or an epoxy resin) can be used.In the case where the third bonding layer 113 is placed on the viewerside (the side of a light emitting device user) when seen from the OLED,a material is required to have light transmittance.

In this embodiment mode, two or more barrier films are formed on thethird substrate 112. Then, a stress relaxing film is provided betweenthe two barrier films. As a result, a sealing film having a laminatestructure of the barrier films and the stress relaxing film is formedbetween the second substrate 112 and the third bonding layer 113.

For example, in this embodiment mode, a film made of silicon nitride isformed as a barrier film 114 a by sputtering on the third substrate 110;a stress relaxing film 114 b containing polyimide is formed on thebarrier film 114 a; and a film made of silicon nitride is formed as abarrier film 114 c by sputtering on the stress relaxing film 114 b. Alaminate film of the barrier film 114 a, the stress relaxing film 114 band the barrier film 114 c is collectively referred to as a sealing film114. Then, the third substrate 112, on which the sealing film 114, isformed is bonded to the element fixed onto the second substrate 110through the third bonding layer 113.

It is sufficient to provide two or more barrier films. As a material ofthe barrier films, silicon nitride, silicon oxynitride, aluminum oxide,aluminum nitride, aluminum oxynitride or aluminum silicide oxynitride(AlSiON) can be used.

Since aluminum silicide oxynitride has a relatively high thermalconductivity, its use for the barrier films allows efficient radiationof heat that is generated in the element.

A resin having light transmittance can be used for the stress relaxingfilm 114 b. Typically, polyimide, acryl, polyamide, polyimide amide,benzocyclobutene, an epoxy resin or the like can be used. In thisembodiment mode, the stress relaxing film is formed by application ofthermally polymerizable polyimide, followed by baking.

A silicon nitride film is formed by introducing argon at a substratetemperature kept at 150° C. under a sputtering pressure of about 0.4 Pa.Film formation is conducted using silicon as a target with introductionof nitrogen and hydrogen in addition to argon. In the case of siliconoxynitride, a film is formed by introducing argon at a substratetemperature kept at 150° C. under a sputtering pressure of about 0.4 Pa.Film formation is conducted using silicon as a target while introducingnitrogen, nitrogen dioxide and hydrogen in addition to argon. Siliconoxide may be alternatively used as a target.

It is desirable that each of the barrier films 114 a and 114 c has athickness in the range of 50 nm to 3 μm. In this embodiment mode, asilicon nitride film is formed to have a thickness of 1 μm.

A method of forming the barrier films is not limited to sputtering; afilm formation method can be suitably determined by those who carry outthe invention. For example, the barrier films may be formed by an LPCVDmethod, a plasma CVD method or the like.

It is desirable that the stress relaxing film 114 b has a thickness inthe range of 200 nm to 2 μm. In this embodiment mode, a polyimide filmis formed to have a thickness of 1 μm as the stress relaxing film.

In this manner, a flexible light emitting device interposed between thetwo flexible substrates 110 and 112 having flexibility can be obtained.With use of the same material for the second substrate 110 and the thirdsubstrate 112, the substrates 110 and 112 have the same thermalexpansion coefficient. As a result, the substrates 110 and 112 can behardly affected by a stress strain due to change in temperature.

The light emitting device manufactured according to this embodiment modeallows the manufacture of an element using a semiconductor (for example,a TFT) without being limited by a heat resistance of the plasticsubstrate. Thus, the light emitting device having extremely highperformance can be obtained.

Although the first bonding layer 102 is made of amorphous silicon and isremoved with a gas containing halogen fluoride in this embodiment mode,the present invention is not limited to this structure. A material and aremoval method of the first bonding layer 102 can be suitably determinedby those who carry out the invention. It is important to determine amaterial and a removal method of the first bonding layer 102 so that thesubstrates, the elements and the films other than the first bondinglayer 102, which are not desired to be removed, are not removed withremoval of the first bonding layer 102 so as not to affect the operationof the light emitting device. It is also important that a material ofthe first bonding layer 102 does not allow its removal in the processother than in the removal step of the first bonding layer 102.

For example, an organic material, which is entirely or partiallyvaporized by radiation of a laser beam, can be used as the first bondinglayer 102. Additionally, it is desirable that a material having laserbeam absorbance, for example, a colored or black material (for example,a resin material containing a black colorant) is used so that a laserbeam is efficiently absorbed only by the first bonding layer 102 in thecase where a second harmonic wave from a YAG laser is used. A material,which is not vaporized in a heat treatment in the element formationsteps, is used for the first bonding layer 102.

Each of the first, second and third bonding layers may be eithersingle-layered or multi-layered. An amorphous silicon film or a DLC filmmay be provided between the bonding layer and the substrate.

The first bonding layer 102 may be formed of an amorphous silicon film,and the first substrate may be peeled off by radiation of a laser beamonto the first bonding layer 102 in the later step. In this case, inorder to facilitate the peeling of the first substrate, it is preferredto use an amorphous silicon film containing a large amount of hydrogen.Hydrogen contained in the amorphous silicon film is vaporized byradiation of a laser beam, so that the first substrate can be easilypeeled off.

As a laser beam, a pulse oscillation or a continuous wave excimer laser,a YAG laser or a YVO₄ laser can be used. A laser beam is radiated ontothe first bonding layer through the first substrate so as to vaporizeonly the first bonding layer to peel off the first substrate. Therefore,as the first substrate, it is preferred to use a substrate through whichat least a radiated laser beam is allowed to pass, typically a substratehaving light transmittance, for example, a glass substrate, a quartzsubstrate or the like, which has a thickness larger than those of thesecond and third substrates.

In the present invention, in order to allow a laser beam to pass throughthe first substrate, it is necessary to suitably select the type of alaser beam and the first substrate. For example, when a quartz substrateis used as the first substrate, a YAG laser (fundamental wave (1064 nm),a second harmonic wave (532 nm), a third harmonic wave (355 nm), and afourth harmonic wave (266 nm)) or an excimer laser (wavelength: 308 nm)is used to form a linear beam which is in turn allowed to pass throughthe quartz substrate. It is noticed that an excimer laser beam does notpass through a glass substrate. Therefore, when a glass substrate isused as the first substrate, a fundamental wave, a second harmonic waveor a third harmonic wave of the YAG laser, preferably, a second harmonicwave (wavelength: 532 nm), is used to form a linear beam which is inturn allowed to pass through the glass substrate.

Alternatively, for example, a method of separating the first substrateby spraying a fluid (a pressure-applied liquid or gas) on the firstbonding layer (typically, a water jet method) may be used.

In the case where the first bonding layer is made of an amorphoussilicon film, the first bonding layer may be removed by using hydrazine.

Alternatively, a method of separating the first substrate by etching,described in Japanese Patent Application Laid-open No. Hei 8-288522, maybe employed. Specifically, an applied silicon oxide film (SOG) may beused as the first bonding layer which is then removed by hydrogenfluoride. In this case, it is important that the silicon oxide film,which is not desired to be removed, is formed to have a fine structurethrough a sputtering or a CVD method so that the silicon oxide filmprovides a high selection ratio when the first bonding layer is to beremoved by hydrogen fluoride.

With such a structure, even if substrates having an extremely smallthickness, specifically, 50 to 300 μm, preferably 150 to 200 μm, areused as the second and third substrates, a light emitting device withhigh reliability can be obtained. It was difficult to form an element onsuch a thin substrate by using a conventionally known manufactureapparatus. However, since the element is formed with being bonded ontothe first substrate, a manufacture apparatus using a thin substrate canbe used without any alteration of the apparatus.

With the use of the sealing film including the multi-layered insulatingfilm, it is possible to effectively restrain the degradation due topenetration of moisture or oxygen. Moreover, a crack is prevented fromoccurring upon bend of the substrate. As a result, a light emittingdevice having enhanced flexibility can be realized.

Embodiment Mode 2

Next, another embodiment mode of the present invention, which differsfrom the above-described first embodiment mode, will be described.

In FIG. 3A, a first bonding layer 202 made of an amorphous silicon filmis formed to have a thickness of 100 to 500 nm (300 nm in thisembodiment mode) is formed on a first substrate 201. Although a glasssubstrate is used as the first substrate 201 in this embodiment mode, aquartz substrate, a silicon substrate, a metal substrate or a ceramicsubstrate may be alternatively used. Any material can be used for thefirst substrate 201 as long as it is resistant to a treatmenttemperature in the later manufacture steps.

As a method of forming the first bonding layer 202, a low pressurethermal CVD method, a plasma CVD method, a sputtering method or anevaporation method may be used. On the first bonding layer 202, aninsulating film 203 made of a silicon oxide film is formed to have athickness of 200 nm. As a method of forming the insulating film 203, alow pressure thermal CVD method, a plasma CVD method, a sputteringmethod or an evaporation method may be employed. The insulating film 203serves to protect an element formed on the first substrate 201 when thefirst bonding layer 202 is removed to peel off the first substrate 201.

Next, an element is formed on the insulating film 203 (FIG. 3B). Theelement herein designates a semiconductor element (typically, a TFT) oran MIM element, which is used as a switching element for a pixel, and anOLED and the like in the case of an active matrix light emitting device.In the case of a passive light emitting device, the element designatesan OLED. In FIG. 3B, a TFT 204 a in a driving circuit 206, TFTs 204 band 204 c and an OLED 205 in a pixel portion are shown as representativeelements.

Then, an insulating film 208 is formed so as to cover theabove-described elements. It is preferred that the insulating film 208has a flatter surface after its formation. It is not necessarilyrequired to provide the insulating film 208.

Next, as shown in FIG. 3C, a second substrate 210 is bonded to the firstsubstrate 201 through a second bonding layer 209. Although a glasssubstrate is used as the second substrate 210 in this embodiment mode, aquartz substrate, a silicon substrate, a metal substrate or a ceramicsubstrate may also be used. Any material may be used for the secondsubstrate 210 as long as the material is resistant to a treatmenttemperature in the later manufacture step.

As a material of the second bonding layer 209, it is necessary to use amaterial which can provide a high selection ratio when the first bondinglayer 202 is to be removed in the later step. Furthermore, for thesecond bonding layer 209, it is required to use such a material that athird bonding layer serving to bond a third substrate is not removedwith the removal of the second bonding layer and does not cause thepeeling of the third substrate. In this embodiment mode, a polyamic acidsolution which is a precursor of a polyimide resin, described inJapanese Patent Application Laid-open No. Hei 5-315630, is used.Specifically, after the second bonding layer 209 is formed to have athickness of 10 to 15 μm using a polyamic acid solution, which is anuncured resin, the second substrate 210 and the interlayer insulatingfilm 208 are bonded to each other through thermocompression bonding.Then, heating is conducted so as to temporarily cure the resin.

In this embodiment mode, a material of the second bonding layer 209 isnot limited to a polyamic acid solution. Any material may be used aslong as it provides a high selection ratio when the first bonding layer202 is to be removed in the later step and the third bonding layer forbonding the third substrate is not removed with the removal of thesecond bonding layer 209 and does not cause the peeling of the thirdsubstrate. It is important that the second bonding layer 209 is made ofsuch a material that is not removed in the steps other than the step ofremoving the second bonding layer 209.

Next, as shown in FIG. 3D, the first substrate 201, the second substrate210 and all the elements and the entire films formed therebetween areexposed to a gas containing halogen fluoride so as to remove the firstbonding layer 202. In this embodiment mode, chlorine trifluoride (ClF₃)is used as halogen fluoride, and nitrogen is used as a diluent gas.Alternatively, argon, helium or neon may be used as a diluent gas. Aflow rate for both gases may be set to 500 sccm (8.35×10⁻⁶ m³/s), and areaction pressure may be set to 1 to 10 Torr (1.3×10² to 1.3×10³ Pa). Atreatment temperature may be a room temperature (typically, 20 to 27°C.).

In this case, the silicon film is etched whereas the plastic film, theglass substrate, the polyimide film, and the silicon oxide film are notetched. More specifically, through exposure to a chlorine trifluoridegas, the first bonding layer 202 is selectively etched to result incomplete removal thereof. Since an active layer of the TFT, which issimilarly made of a silicon film, is not exposed to the outside, theactive layer is not exposed to a chlorine trifluoride gas and thereforeis not etched.

In this embodiment mode, the first bonding layer 202 is gradually etchedfrom its exposed edge portions. The first substrate 201 and theinsulating film 203 are separated from each other when the first bondinglayer 202 is completely removed. After removal of the first bondinglayer 202, the TFTs and the OLED, each of which includes a laminate ofthin films, remain on the second substrate 210.

A large substrate is not preferred as the first substrate 201 becausethe first bonding layer 202 is gradually etched from its edges and thetime required for completely removing the first bonding layer 202 getslong with increase in size. Therefore, it is desirable that thisembodiment mode is carried out for the first substrate 201 having adiagonal of 3 inches or less (preferably, 1 inch or less).

After removal of the first substrate 201 in this manner, a third bondinglayer 213 is formed as shown in FIG. 4A. Then, a third substrate 212 isbonded to the second substrate 212 through the third bonding layer 213.In this embodiment mode, a plastic substrate is used as the thirdsubstrate 212. More specifically, a resin substrate having a thicknessof 10 μm or more, for example, a substrate made of PES (polyethersulfone), PC (polycarbonate), PET (polyethylene terephthalate) or PEN(polyethylene naphthalate) can be used as the third substrate 212.

An insulating film made of a resin (typically, polyimide, acryl,polyamide or an epoxy resin) can be used as the third bonding layer 213.In the case where the third bonding layer 213 is placed on the viewerside (the side of a light emitting device user) when seen from the OLED,a material is required to have light transmittance.

Furthermore, in this embodiment mode, two or more barrier films areformed on the third substrate 212. Then, a stress relaxing film isprovided between the two barrier films. As a result, a sealing filmhaving a laminate structure of the barrier films and the stress relaxingfilm is formed between the third substrate 212 and the third bondinglayer 213.

For example, in this embodiment mode, a film made of silicon nitride isformed as a barrier film 214 a by sputtering on the third substrate 212;a stress relaxing film 214 b containing polyimide is formed on thebarrier film 214 a; and a film made of silicon nitride is formed as abarrier film 214 c by sputtering on the stress relaxing film 214 b. Alaminate film of the barrier film 214 a, the stress relaxing film 214 band the barrier film 214 c is collectively referred to as a sealing film214. Then, the third substrate 212, on which the sealing film 214 isformed, is bonded to the element fixed onto the second substrate 210through the third bonding layer 213.

It is sufficient to provide two or more barrier films. As a material ofthe barrier films, silicon nitride, silicon oxynitride, aluminum oxide,aluminum nitride, aluminum oxynitride or aluminum silicide oxynitride(AlSiON) can be used.

Since aluminum silicide oxynitride has a relatively high thermalconductivity, its use for the barrier films allows efficient radiationof heat that is generated in the element.

A resin having light transmittance can be used for the stress relaxingfilm 214 b. Typically, polyimide, acryl, polyamide, polyimide amide,benzocyclobutene, an epoxy resin or the like can be used. In thisembodiment mode, the stress relaxing film is formed by application ofacryl, followed by baking.

A silicon nitride film is formed by introducing argon at a substratetemperature kept at 150° C. under a sputtering pressure of about 0.4 Pa.Film formation is conducted using silicon as a target while introducingnitrogen and hydrogen in addition to argon. In the case of siliconoxynitride, a film is formed by introducing argon at a substratetemperature kept at 150° C. under a sputtering pressure of about 0.4 Pa.Film formation is conducted using silicon as a target while introducingnitrogen, nitrogen dioxide and hydrogen in addition to argon. Siliconoxide may be alternatively used as a target.

It is desirable that each of the barrier films 214 a and 214 c has athickness in the range of 50 nm to 3 μm. In this embodiment mode, asilicon nitride film is formed to have a thickness of 1 μm.

A method of forming the barrier films is not limited to sputtering; afilm formation method can be suitably determined by those who carry outthe invention. For example, the barrier films may be formed by an LPCVDmethod, a plasma CVD method or the like.

It is desirable that the stress relaxing film 214 b has a thickness inthe range of is 200 nm to 2 μm. In this embodiment mode, an acryl filmis formed to have a thickness of 1 μm.

Next, as shown in FIG. 4B, the second bonding layer 209 is removed topeel off the second substrate 210. More specifically, the second bondinglayer 209 is removed by being dipped into water for about an hour,thereby allowing the second substrate 210 to be peeled off.

It is important to select a method of peeling off the second bondinglayer 209 according to a material of the second bonding layer 209, amaterial of the element or the films, a material of the substrate, andthe like.

Next, as shown in FIG. 4C, barrier films in two or more layers areprovided on the side where the second substrate 210 is peeled off, thatis, on the side opposite to the third substrate through the OLED. Then,a stress relaxing film is provided between the two barrier films.

In this embodiment mode, for example, on the side of the insulating film208 opposite to the side being in contact with the second substrate 210,a film made of silicon nitride is formed as a barrier film 215 a bysputtering; a stress relaxing film 215 b containing polyimide is formedon the barrier film 215 a; and a film made of silicon nitride is formedas a barrier film 215 c by sputtering on the stress relaxing film 215 b.A laminate film of the barrier film 215 a, the stress relaxing film 215b and the barrier film 215 c is collectively referred to as a sealingfilm 215.

It is sufficient to provide two or more barrier films. As a material ofthe barrier films, silicon nitride, silicon oxynitride, aluminum oxide,aluminum nitride, aluminum oxynitride or aluminum silicide oxynitride(AlSiON) can be used.

Since aluminum silicide oxynitride has a relatively high thermalconductivity, its use for the barrier films allows efficient radiationof heat that is generated in the element.

A resin having light transmittance can be used for the stress relaxingfilm 215 b. Typically, polyimide, acryl, polyamide, polyimide amide,benzocyclobutene, an epoxy resin or the like can be used. In thisembodiment mode, the stress relaxing film is formed by application ofacryl, followed by baking.

A silicon nitride film is formed by introducing argon at a substratetemperature kept at 150° C. under a sputtering pressure of about 0.4 Pa.Film formation is conducted using silicon as a target while introducingnitrogen and hydrogen in addition to argon. In the case of siliconoxynitride, a film is formed by introducing argon at a substratetemperature kept at 150° C. under a sputtering pressure of about 0.4 Pa.Film formation is conducted using silicon as a target while introducingnitrogen, nitrogen dioxide and hydrogen in addition to argon. Siliconoxide may be alternatively used as a target.

It is desirable that each of the barrier films 215 a and 215 c has athickness in the range of 50 nm to 3 μm. In this embodiment mode, asilicon nitride film is formed to have a thickness of 1 μm.

A method of forming the barrier films is not limited to sputtering; afilm formation method can be suitably determined by those who carry outthe invention. For example, a film may be formed by an LPCVD method, aplasma CVD method or the like.

It is desirable that the stress relaxing film 215 b has a thickness inthe range of 200 nm to 2 μm. In this embodiment mode, an acryl film isformed to have a thickness of 1 μm.

In this manner, a flexible light emitting device using a single plasticsubstrate 212 can be obtained.

Since an element using a semiconductor (for example, a TFT) can beformed without being limited by a heat resistance of the plasticsubstrate, the light emitting device having extremely high performancecan be manufactured according to this embodiment mode.

Although the first bonding layer 202 is made of amorphous silicon, andis removed with a gas containing halogen fluoride in this embodimentmode, the present invention is not limited to this structure. A materialand a removal method of the first bonding layer 202 can be suitablydetermined by those who carry out the invention. It is important todetermine a material and a removal method of the first bonding layer 202so that the substrates, the other bonding layers, the elements and thefilms other than the first bonding layer 202, which are not desired tobe removed, are not removed with removal of the first bonding layer 202so as not to affect the operation of the light emitting device. It isalso important that a material of the first bonding layer 202 does notallow its removal in the process other than the removal step of thefirst bonding layer 202.

Although a polyamic acid solution, which is a precursor of a polyimideresin, is used for the second bonding layer 209 which is then removedwith water, the structure of the present invention is not limitedthereto. A material and a removal method of the second bonding layer 209can be suitably determined by those who carry out the invention. It isimportant to determine a material and a removal method of the secondbonding layer 209 so that the substrates, the other bonding layers, theelements and the films other than the second bonding layer 209, whichare not desired to be removed, are not removed with removal of thesecond bonding layer 209 so as not to affect the operation of the lightemitting device. It is also important that a material of the secondbonding layer 209 does not allow its removal in the process other thanthe removal step of the second bonding layer 209.

For example, an organic material, which is entirely or partiallyvaporized by radiation of a laser beam, can be used for the first andsecond bonding layers 202 and 209. Additionally, it is desirable that amaterial having laser beam absorbance, for example, a colored or blackmaterial (for example, a resin material containing a black colorant) isused so that a laser beam is efficiently absorbed only by the first andsecond bonding layers 202 and 209 in the case where a second harmonicwave from a YAG laser is used. The first and second bonding layers 202and 209, which are not vaporized in a heat treatment in the elementformation steps, are employed.

Each of the first, second and third bonding layers may be eithersingle-layered or multi-layered. An amorphous silicon film or a DLC filmmay be provided between the bonding layer and the substrate.

The first bonding layer 202 or the second bonding layer 209 may beformed of an amorphous silicon film, and the substrate may be peeled offby radiation of a laser beam onto the first bonding layer 202 or thesecond bonding layer 209 in the later step. In this case, in order tofacilitate the peeling of the first substrate, it is preferred to use anamorphous silicon film containing a large amount of hydrogen. Hydrogencontained in the amorphous silicon film is vaporized by radiation of alaser beam, so that the substrate can be easily peeled off.

As a laser beam, a pulse oscillation or a continuous wave excimer laser,a YAG laser or a YVO₄ laser can be used. In the case where the firstsubstrate is to be peeled off, a laser beam is radiated onto the firstbonding layer through the first substrate so as to vaporize only thefirst bonding layer to peel off the first substrate. In the case wherethe second substrate is to be peeled off, a laser beam is radiated ontothe second bonding layer through the second substrate so as to vaporizeonly the second bonding layer to peel off the second substrate.Therefore, as the first or second substrate, it is preferred to use asubstrate having a thickness larger than that of the third substrates,which allows at least a radiated laser beam to pass through, typically asubstrate having light transmittance, for example, a glass substrate, aquartz substrate or the like.

In the present invention, in order to allow a laser beam to pass throughthe first or second substrate, it is necessary to suitably select thetype of a laser beam and the type of the first substrate. For example,when a quartz substrate is used as the first substrate, a YAG laser(fundamental wave (1064 nm), a second harmonic wave (532 nm), a thirdharmonic wave (355 nm), and a fourth harmonic wave (266 nm)) or anexcimer laser (wavelength: 308 nm) is used to form a linear beam whichis in turn allowed to pass through the quartz substrate. It is noticedthat an excimer laser beam does not passes through a glass substrate.Therefore, when a glass substrate is used, a fundamental wave, a secondharmonic wave or a third harmonic wave of the YAG laser, preferably, asecond harmonic wave (wavelength: 532 nm), is used to form a linear beamwhich is in turn allowed to pass through the glass substrate.

Alternatively, for example, a method of separating the first substrateby spraying a fluid (a pressure-applied liquid or gas) on the firstbonding layer (typically, a water jet method) may be used.

In the case where the first bonding layer is made of an amorphoussilicon film, the first bonding layer may be removed by using hydrazine.

Alternatively, a method of separating the first substrate by etching,described in Japanese Patent Application Laid-open No. Hei 8-288522, maybe used. Specifically, an applied silicon oxide film (SOG) may be usedas the first or second bonding layer which is then removed by hydrogenfluoride. In this case, it is important that the silicon oxide film,which is not desired to be removed, is formed to have a fine structurethrough a sputtering or a CVD method so that the silicon oxide filmprovides a high selection ratio when the first or second bonding layeris to be removed by hydrogen fluoride.

With such a structure, even if a substrate having an extremely smallthickness, specifically, 50 to 300 μm, preferably 150 to 200 μm is usedas the third substrate, a light emitting device with high reliabilitycan be obtained. It is difficult to form an element on such a thinsubstrate by using a conventionally known manufacture apparatus.However, since the element is formed with being bonded onto the firstand second substrates, a manufacturing apparatus using a thin substratecan be used without any alteration of the apparatus.

With the use of the sealing film including the multi-layered insulatingfilm, it is possible to effectively restrain the degradation due topenetration of moisture or oxygen. Moreover, a crack is prevented fromoccurring upon bend of the substrate. As a result, a light emittingdevice having enhanced flexibility can be realized.

In the first and second embodiment modes, either an anode or a cathodeof the OLED may be used as a pixel electrode.

EMBODIMENTS

Hereinafter, embodiments of the present invention will be described.

Embodiment 1

In Embodiment 1, the outward appearance of a light emitting deviceaccording to the present invention and its connection to an FPC will bedescribed.

FIG. 5A shows an example of a top view of a light emitting deviceaccording to the present invention, described in Embodiment mode 1. Asecond substrate 301 and a third substrate 302 are both plasticsubstrates having flexibility. A pixel portion 303 and driving circuits(a source-side driving circuit 304 and a gate-side driving circuit 305)are provided between the second substrate 301 and the third substrate302.

In FIG. 5A, there is shown an example where the source-side drivingcircuit 304 and the gate side-driving circuit 305 are formed on thesubstrate on which the pixel portion 303 is also formed. However, thedriving circuits represented by the source-side driving circuit 304 andthe gate side-driving circuit 305 may be formed on a different substratefrom the substrate on which the pixel portion 303 is formed. In thiscase, the driving circuits may be connected to the pixel portion 303 viaan FPC or the like.

The number and the arrangement of the source-side driving circuit 304and the gate-side driving circuit 305 are not limited to the structureshown in FIG. 5A.

The reference symbol 306 designates an FPC, via which a signal from anIC including a controller or a source voltage are supplied to the pixelportion 303, the source-side driving circuit 304 and the gate-sidedriving circuit 305.

FIG. 5B is an enlarged view of a portion surrounded by a dot line inFIG. 5A where the FPC 306 and the second substrate 301 are connected toeach other. FIG. 5C is a cross-sectional view taken along a line A-A′ inFIG. 5B.

Wirings 310, which are extended so as to supply a signal or a sourcevoltage to the pixel portion 303, the source-side driving circuit 304and the gate-side driving circuit 305, are provided between the secondsubstrate 301 and the third substrate 302. Terminals 311 are providedfor the FPC 306.

The second substrate 301 and various films such as a sealing film and aninsulating film provided between the second substrate 301 and theextended wirings 310 are partially removed by a laser beam or the liketo provide contact holes 313. Therefore, a plurality of the extendedwirings 310 are exposed through the contact holes 313, and arerespectively connected to the terminals 311 through a conductive resin312 having anisotropy.

Although there is shown the example where the extended wirings 310 arepartially exposed from the side of the second substrate 301 in FIGS. 5Ato 5C, the present invention is not limited thereto. Alternatively, theextended wirings may be partially exposed from the side of the thirdsubstrate 302.

FIG. 6A shows the light emitting device shown in FIG. 5A in a bentstate. Since the second substrate and the third substrate of the lightemitting device described in Embodiment mode 1 both have flexibility,the light emitting device can be bent to a certain degree as shown inFIG. 6A. Thus, such a light emitting device has a wide range ofapplications because it can be used for a display having a curvedsurface, a show window and the like. Moreover, not only the lightemitting device described in Embodiment mode 1 but also the lightemitting device described in Embodiment mode 2 can be similarly bent.

FIG. 6B is a cross-sectional view of the light emitting device shown inFIG. 6A. A plurality of elements are formed between the second substrate301 and the third substrate 302. Herein, TFTs 303 a, 303 b and 303 c andan OLED 304 are representatively shown. A broken line 309 represents acenter line between the second substrate 301 and the third substrate302.

A barrier film 306 a, a stress relaxing film 306 b and a barrier film306 c (collectively referred to as a sealing film 306) are providedbetween the second substrate 301 and a plurality of the elements. Abarrier film 307 a, a stress relaxing film 307 b and a barrier film 307c (collectively referred to as a sealing film 307) are provided betweenthe third substrate 302 and a plurality of the elements.

Furthermore, a second bonding layer 305 is provided between the sealingfilm 306 and a plurality of the elements, whereas a third bonding layer308 is provided between the sealing film 307 and a plurality of theelements.

Next, the connection of the light emitting device described inEmbodiment mode 2 to the FPC will be described. FIG. 7 is across-sectional view showing a portion where the light emitting devicedescribed in Embodiment mode 2 and the FPC are connected to each other.

A wiring 403 for extension is provided on a third substrate 401. Asealing film 402 is formed so as to cover the wiring 403 for extensionand a plurality of elements provided on the third substrate 401.Although the sealing film 402 is shown as a single-layered film in FIG.7, the sealing film practically includes a plurality of barrier filmsand a stress relaxing film interposed therebetween.

Various films such as the sealing film 402 and an insulating filmprovided between the third substrate 401 and the extended wring 403 arepartially removed by a laser beam or the like to provide a contact hole.Therefore, the extended wiring 403 is exposed through the contact hole,and is electrically connected to a terminal 405 included in an FPC 404through a conductive resin 406 having anisotropy.

Although there is shown the example where the extended wiring ispartially exposed from the side of the sealing film 402 in FIG. 7, thepresent invention is not limited thereto. Alternatively, the extendedwiring may be partially exposed from the side of the third substrate.

Embodiment 2

In Embodiment 2, an example of Embodiment mode 1 according to thepresent invention will be described.

In FIG. 8A, a first bonding layer 502 made of an applied silicon oxidefilm (SOG) is formed to have a thickness of 100 to 500 nm (300 nm inthis embodiment) is formed on a first substrate 501. Although a glasssubstrate is used as the first substrate 501 in this embodiment, aquartz substrate, a silicon substrate, a metal substrate or a ceramicsubstrate may be alternatively used. Any material can be used for thefirst substrate 501 as long as it is resistant to a treatmenttemperature in the later manufacturing steps.

As a method of forming the SOG film, an iodine solution is added to anSOG solution by spin coating, which is then dried to desorb iodinetherefrom. Then, a thermal treatment at about 400° C. is conducted toform the SOG film. In this embodiment, the SOG film having a thicknessof 100 nm is formed. A method of forming the SOG film as the firstbonding layer 502 is not limited to the above method. Both an organicSOG and an inorganic SOG may be used as the SOG; any SOG can be used aslong as it can be removed with hydrogen fluoride in the later step. Itis important that the silicon oxide film, which is not desired to beremoved, is formed to have a fine structure by sputtering or a CVDmethod so as to provide a high selection ratio when the first bondinglayer is to be removed with hydrogen fluoride.

Next, a protection film made of Al is formed on the first bonding layer502 by a low pressure thermal CVD method, a plasma CVD method, asputtering method or an evaporation method. In this embodiment, aprotection film 503 made of Al is formed to have a thickness of 200 nmon the first bonding layer 502 by sputtering.

Although Al is used as a material of the protection film 503 in thisembodiment, the present invention is not limited thereto. It isimportant to select such a material that is not removed with removal ofthe first bonding layer 502 and that is not removed in the process otherthan in the step of removing the protection film 503. Furthermore, it isimportant that such a material does not allow removal of the other filmsand the substrates in the step of removing the protection film 503. Theprotection film 503 serves to protect an element formed on the firstsubstrate 501 when the first bonding layer 502 is removed to peel offthe first substrate 501.

Next, an element is formed on the protection film 503 (FIG. 8B). In FIG.5B, TFTs 504 a and 504 b in a driving circuit are shown asrepresentative elements.

In this embodiment, the TFT 504 a is an n-channel TFT whereas the TFT504 b is a p-channel TFT. The TFTs 504 a and 504 b form a CMOS.

The TFr504 a includes a first electrode 550 formed on the protectionfilm 503, an insulating film 551 formed so as to cover the firstelectrode 550, a semiconductor film 552 formed so as to be in contactwith the insulating film 551, an insulating film 553 formed so as to bein contact with the semiconductor film 552, and a second electrode 554in contact with the insulating film 553.

The TFT504 b includes a first electrode 560, the insulating film 551formed so as to cover the first electrode 560, a semiconductor film 562formed so as to be in contact with the insulating film 551, theinsulating film 553 formed so as to be in contact with the semiconductorfilm 562, and a second electrode 564 in contact with the insulating film553.

A terminal 570, which is formed simultaneously with the first electrodes550 and 560, is provided on the protection film 503.

Then, an insulating film 565 is formed so as to cover the TFTs 504 a and504 b. A wiring 571 being in contact with the semiconductor film 552 andthe terminal 570, a wiring 572 being in contact with the semiconductorfilms 552 and 562, and a wiring 573 being in contact with thesemiconductor film 562 are formed via contact holes formed through theinsulating films 565, 551 and 553.

An insulating film 574 is formed so as to cover the wirings 571, 572 and573 and the insulating film 565. Although not shown, an OLED is formedon the insulating film 574.

Then, an insulating film 508 is formed so as to cover these elements. Itis preferred that the insulating film 508 has a flatter surface afterits formation. The insulating film 508 is not necessarily formed.

Next, as shown in FIG. 8C, a second substrate 510 is bonded to the firstsubstrate through a second bonding layer 509. A plastic substrate isused as the second substrate 510 in this embodiment. More specifically,a resin substrate having a thickness of 10 μm or more, for example, asubstrate made of PES (polyether sulfone), PC (polycarbonate), PET(polyethylene terephthalate) or PEN (polyethylene naphthalate) can beused as the second substrate 510.

As a material of the second bonding layer 509, it is necessary to use amaterial which can provide a high selection ratio when the first bondinglayer 502 is to be removed in the later step. Typically, an insulatingfilm made of a resin can be used. Although polyimide is used in thisembodiment, acryl, polyamide or an epoxy resin can also be used. In thecase where the second bonding layer 509 is placed on the viewer side(the side of a light emitting device user) when seen from the OLED, amaterial is required to have light transmittance.

Furthermore, in this embodiment, two or more barrier films are formed onthe second substrate 510. Then, a stress relaxing film is providedbetween the two barrier films. As a result, a sealing film having alaminate structure of the barrier films and the stress relaxing film isformed between the second substrate 510 and the second bonding layer509.

For example, in this embodiment, a film made of silicon nitride isformed as a barrier film 511 a by sputtering on the second substrate510; a stress relaxing film 511 b containing polyimide is formed on thebarrier film 511 a; and a film made of silicon nitride is formed as abarrier film 511 c by sputtering on the stress relaxing film 511 b. Alaminate film of the barrier film 511 a, the stress relaxing film 511 band the barrier film 511 c is collectively referred to as a sealing film511. Then, the second substrate 510, on which the sealing film 511 isformed, is bonded to the element formed on the first substrate throughthe second bonding layer 509.

It is sufficient to provide two or more barrier films. As a material ofthe barrier films, silicon nitride, silicon oxynitride, aluminum oxide,aluminum nitride, aluminum oxynitride or aluminum silicide oxynitride(AlSiON) can be used.

A resin having light transmittance can be used for the stress relaxingfilm 511 b. Typically, polyimide, acryl, polyamide, polyimide amide,benzocyclobutene, an epoxy resin or the like can be used. In thisembodiment, the stress relaxing film is formed by application ofthermally polymerizable polyimide, followed by baking.

A silicon nitride film is formed while introducing argon at a substratetemperature kept at 150° C. under a sputtering pressure of about 0.4 Pa.Film formation is conducted using silicon as a target while introducingnitrogen and hydrogen in addition to argon. In the case of siliconoxynitride, a film is formed by introducing argon at a substratetemperature kept at 150° C. under a sputtering pressure of about 0.4 Pa.Film formation is conducted using silicon as a target while introducingnitrogen, nitrogen dioxide and hydrogen in addition to argon. Siliconoxide may be alternatively used as a target.

It is desirable that each of the barrier films 511 a and 511 c has athickness in the range of 50 nm to 3 μm. In this embodiment, a siliconnitride film is formed to have a thickness of 1 μm.

A method of forming the barrier films is not limited to sputtering; afilm formation method can be suitably determined by those who carry outthe invention. For example, a film may be formed by an LPCVD method, aplasma CVD method or the like.

It is desirable that the stress relaxing film 511 b has a thickness inthe range of 200 nm to 2 μm. In this embodiment, a polyimide film isformed to have a thickness of 1 μm.

For the first and second barrier layers 511 a and 511 c and the stressrelaxing layer 511 b, it is necessary to use materials which provide ahigh selection ratio when the first bonding layer 502 is to be removedin the later step.

Owing to the process shown in FIG. 8C, the OLED can be completelyisolated from air. As a result, the degradation of the organic lightemitting material due to oxidation can be substantially completelyrestrained, thereby remarkably improving the reliability of the OLED.

Next, as shown in FIG. 8D, the first bonding layer 502 is removed withhydrogen fluoride. In this embodiment, the first and second substrates501 and 510, and all the elements and the entire films formedtherebetween are dipped into buffered hydrofluoric acid (HF/NH₄F=0.01 to0.2, for example, 0.1) so as to remove the first bonding layer 502.

Since the silicon oxide film, which is not desired to be removed, ismade of a fine film formed by sputtering or a CVD method, only the firstbonding layer is removed with hydrogen fluoride.

In the case of this embodiment, the first bonding layer 502 is graduallyetched from its exposed edge portions. The first substrate 501 and theprotection film 503 are separated from each other when the first bondinglayer 502 is completely removed. After removal of the first bondinglayer 502, the TFTs and the OLED, each of which includes a laminate ofthin films, remain on the second substrate 510.

A large substrate is not preferred as the first substrate 501 becausethe time required for completely removing the first bonding layer 502from its edges gets long with increase in size of the first substrate.Therefore, it is desirable that this embodiment is carried out for thefirst substrate 501 having a diagonal of 3 inches or less (preferably, 1inch or less).

Next, as shown in FIG. 9A, the protection film 503 is removed. In thisembodiment, the protection film 503 made of Al is removed by wet etchingwith a phosphoric acid type etchant so as to expose the terminal 570 andthe first electrodes 550 and 560.

Then, as shown in FIG. 9B, a third bonding layer 513 made of aconductive resin having anisotropy is formed. Through the third bondinglayer 513, the third substrate 512 is attached to the side where theterminal 570 and the first electrodes 550 and 560 are exposed.

In this embodiment, a plastic substrate is used as the third substrate512. More specifically, a resin substrate having a thickness of 10 μm ormore, for example, a substrate made of PES (polyether sulfone), PC(polycarbonate), PET (polyethylene terephthalate) or PEN (polyethylenenaphthalate) can be used as the third substrate 512.

As the third bonding layer 513, an insulating film made of a resin(typically, polyimide, acryl, polyamide or an epoxy resin) can be used.In the case where the third bonding layer 513 is placed on the viewerside when seen from the OLED, a material is required to have lighttransmittance.

In this embodiment, two or more barrier films are formed on the thirdsubstrate 512. Then, a stress relaxing film is provided between the twobarrier films. As a result, a sealing film having a laminate structureof the barrier films and the stress relaxing film is formed between thethird substrate 512 and the third bonding layer 513.

For example, in this embodiment, a film made of silicon nitride isformed as a barrier film 514 a by sputtering on the third substrate 512;a stress relaxing film 514 b containing polyimide is formed on thebarrier film 514 a; and a film made of silicon nitride is formed as abarrier film 514 c by sputtering on the stress relaxing film 514 b. Alaminate film of the barrier film 514 a, the stress relaxing film 514 band the barrier film 514 c is collectively referred to as a sealing film514. Then, the third substrate 512, on which the sealing film 514 isformed, is bonded to the element fixed onto the second substrate 510through the third bonding layer 513.

It is sufficient to provide two or more barrier films. As a material ofthe barrier films, silicon nitride, silicon oxynitride, aluminum oxide,aluminum nitride, aluminum oxynitride or aluminum silicide oxynitride(AlSiON) can be used.

A resin having light transmittance can be used for the stress relaxingfilm 514 b. Typically, polyimide, acryl, polyamide, polyimide amide,benzocyclobutene, an epoxy resin or the like can be used. In thisembodiment, the stress relaxing film is formed by application ofthermally polymerizable polyimide, followed by baking.

A silicon nitride film is formed by introducing argon at a substratetemperature kept at 150° C. under a sputtering pressure of about 0.4 Pa.Film formation is conducted using silicon as a target while introducingnitrogen and hydrogen in addition to argon. In the case of siliconoxynitride, a film is formed by introducing argon at a substratetemperature kept at 150° C. under a sputtering pressure of about 0.4 Pa.Film formation is conducted using silicon as a target while introducingnitrogen, nitrogen dioxide and hydrogen in addition to argon. Siliconoxide may be alternatively used as a target.

It is desirable that each of the barrier films 514 a and 514 c has athickness in the range of 50 nm to 3 μm. In this embodiment, a siliconnitride film is formed to have a thickness of 1 μm.

A method of forming the barrier films is not limited to sputtering; afilm formation method can be suitably determined by those who carry outthe invention. For example, a film may be formed by an LPCVD method, aplasma CVD method or the like.

It is desirable that the stress relaxing film 514 b has a thickness inthe range of 200 nm to 2 μm. In this embodiment, a polyimide film isformed to have a thickness of 1 μm.

Then, a contact hole is formed through the third substrate 512 and thesealing film 514 by radiation of a laser beam or the like. Al isevaporated on a portion of the third substrate 512 where the contacthole is formed and the periphery thereof, thereby forming terminals 580and 581 on the respective surfaces of the third substrate 512, which areelectrically connected to each other. A method of forming the terminals580 and 581 is not limited to the above-mentioned structure.

The terminal 580 formed on the third substrate 512 is electricallyconnected through the third bonding layer 513 to the terminal 570 thatis formed simultaneously with the first electrodes 550 and 560.

In this manner, a flexible light emitting device interposed between theplastic substrates 510 and 512 can be obtained. With the use of the samematerial for the second substrate 510 and the third substrate 512, thesubstrates 510 and 512 have the same thermal expansion coefficient. As aresult, the substrates 510 and 512 can be hardly affected by a stressstrain due to change in temperature.

As shown in FIG. 9C, the terminal 581 formed so as not to be in contactwith the third bonding layer 513 but to be in contact with the thirdsubstrate 512 and the terminal 591 included in an FPC 590 are connectedto each other through a fourth bonding layer 592 made of an electricallyconductive resin having anisotropy.

The light emitting device manufactured according to this embodimentallows the manufacture of an element employing a semiconductor (forexample, a TFT) without being limited by a heat resistance of theplastic substrate. Thus, the light emitting device having extremely highperformance can be obtained.

Although the first bonding layer 502 is made of SOG and is removed withhydrogen fluoride in this embodiment, the present invention is notlimited to this structure. A material and a removal method of the firstbonding layer 502 can be suitably determined by those who carry out theinvention. It is important to determine a material and a removal methodof the first bonding layer 502 so that the substrates, the element andthe films other than the first bonding layer 502, which are not desiredto be removed, are not removed with removal of the first bonding layer502 and does not affect the operation of the light emitting device.Moreover, it is also important that a material of the first bondinglayer 502 does not allow its removal in the process other than theremoval step of the first bonding layer 502.

For example, an organic material, which is entirely or partiallyvaporized by radiation of a laser beam, can be used as the first bondinglayer 502. Additionally, it is desirable that a material having laserbeam absorbance, for example, a colored or black material (for example,a resin material containing a black colorant) is used so that a laserbeam is efficiently absorbed only by the first bonding layer 502 in thecase where a second harmonic wave from a YAG laser is used. The firstbonding layer 502, which is not vaporized in a heat treatment in theelement formation steps, is used.

Each of the first, second and third bonding layers may be eithersingle-layered or multi-layered. An amorphous silicon film or a DLC filmmay be provided between the bonding layer and the substrate.

The first bonding layer 502 may be formed of an amorphous silicon film,and in the later step, the first substrate may be peeled off byradiation of a laser beam onto the first bonding layer 502. In thiscase, in order to facilitate the peeling of the first substrate, it ispreferred to use an amorphous silicon film containing a large amount ofhydrogen. Hydrogen contained in the amorphous silicon film is vaporizedby radiation of a laser beam, so that the first substrate can be easilypeeled off.

As a laser beam, a pulse or a continuous wave excimer laser, a YAG laseror a YVO₄ laser can be used. A laser beam is radiated onto the firstbonding layer through the first substrate so as to vaporize only thefirst bonding layer to peel off the first substrate. Therefore, as thefirst substrate, it is preferred to use a substrate having a thicknesslarger than that of the second and third substrates, which allows atleast a radiated laser beam to pass through, typically a substratehaving light transmittance, for example, a glass substrate, a quartzsubstrate or the like.

In the present invention, in order to allow a laser beam to pass throughthe first substrate, it is necessary to suitably select the type of alaser beam and the first substrate. For example, when a quartz substrateis used as the first substrate, a YAG laser (fundamental wave (1064 nm),a second harmonic wave (532 nm), a third harmonic wave (355 nm), and afourth harmonic wave (266 nm)) or an excimer laser (wavelength: 308 nm)is used to form a linear beam which is in turn allowed to pass throughthe quartz substrate. It is noticed that an excimer laser beam does notpass through a glass substrate. Therefore, when a glass substrate isused as the first substrate, a fundamental wave, a second harmonic waveor a third harmonic wave of the YAG laser, preferably, a second harmonicwave (wavelength: 532 nm), is used to form a linear beam which is inturn allowed to pass through the glass substrate.

Alternatively, a method of separating the first substrate by spraying afluid (a pressure-applied liquid or gas) on the first bonding layer(typically, a water jet method) or a combination with this method can beused.

In the case where the first bonding layer is made of an amorphoussilicon film, the first bonding layer may be removed by using hydrazine.

Alternatively, a method of separating the first substrate by etching,described in JP 8-288522 A, may be used. Specifically, an appliedsilicon oxide film (SOG) may be used as the first bonding layer which isremoved by hydrogen fluoride. In this case, it is important that thesilicon oxide film, which is not desired to be removed, is formed tohave a fine structure through a sputtering or a CVD method so that thesilicon oxide film provides a high selection ratio when the firstbonding layer is to be removed with hydrogen fluoride.

With such a structure, even if substrates having an extremely smallthickness, specifically, 50 to 300 μm, preferably 150 to 200 μm are usedas the second and third substrates, a light emitting device with highreliability can be obtained. It was difficult to form an element on sucha thin substrate by using a conventionally known manufacturingapparatus. However, since the element is formed with being bonded ontothe first substrate, a manufacturing apparatus can be used with the useof a thick substrate without any alteration of the apparatus.

With the use of the sealing film including the multi-layered insulatingfilm, it is possible to effectively restrain the degradation due topenetration of moisture or oxygen. Moreover, a crack is prevented fromoccurring upon bend of the substrate. As a result, a light emittingdevice having enhanced flexibility can be realized.

Embodiment 3

In this embodiment, a method of forming TFT of a driving circuit (asource signal line driver circuit and a gate signal line driver circuit)arranged in the periphery of the pixel portion and a pixel portion willbe explained in detail. In this embodiment, in relation to the drivercircuit, CMOS circuit is only shown as a basic unit for briefdescription.

First, as shown in FIG. 10A, a first bonding film 5001 formed ofamorphous silicon film is formed and having a thickness of from 100 to500 nm (preferably 300 nm) on a first substrate 5000 formed of glasssuch as barium borosilicate glass or alumino borosilicate glassrepresented by #7059 glass and #1737 glass of CORNING Corporation, etc.The first bonding film 5001 is formed by using a low pressure CVDmethod, plasma CVD method, sputtering method or evaporation method canbe used. The first bonding film 5001 is formed by using sputteringmethod in this embodiment.

Next, a base film 5002 formed of an insulating film such as a siliconoxide film, a silicon oxynitride film or a silicon nitride oxide film isformed on the first bonding film 5001. The base film 5002 has an effectof protecting an element formed on a substrate 5000 when the firstbonding layer 5001 is removed to peel off the substrate 5000. Forexample, a silicon nitride oxide film formed from SiH₄, NH₃ and N₂O bythe plasma CVD method and having a thickness of from 10 to 200 nm(preferably 50 to 100 nm) is formed. Similarly, a hydrogenerated siliconnitride oxide film formed from SiH₄ and N₂O and having a thickness offrom 50 to 200 nm (preferably 100 to 150 nm) is layered thereon. In thisembodiment, the base film 5002 has a two-layer structure, but may alsobe formed as a single layer film of one of the above insulating films,or a laminate film having more than two layers of the above insulatingfilms.

Island-like semiconductor layers 5003 to 5006 are formed from acrystalline semiconductor film obtained by conducting lasercrystallization or a known thermal crystallization on a semiconductorfilm having an amorphous structure. These island-like semiconductorlayers 5003 to 5006 each have a thickness of from 25 to 80 nm(preferably 30 to 60 nm). No limitation is put on the material of thecrystalline semiconductor film, but the crystalline semiconductor filmis preferably formed from silicon, a silicon germanium (SiGe) alloy,etc.

When the crystalline semiconductor film is to be manufactured by thelaser crystallization method, an excimer laser, a YAG laser and an YVO₄laser of a pulse oscillation type or continuous light emitting type areused. When these lasers are used, it is preferable to use a method inwhich a laser beam radiated from a laser emitting device is convergedinto a linear shape by an optical system and then is irradiated to thesemiconductor film. A crystallization condition is suitably selected byan operator. When the excimer laser is used, pulse oscillation frequencyis set to 300 Hz, and laser energy density is set to from 100 to 400mJ/cm² (typically 200 to 300 mJ/cm². When the YAG laser is used, pulseoscillation frequency is preferably set to from 30 to 300 kHz by usingits second harmonic, and laser energy density is preferably set to from300 to 600 mJ/cm² (typically 350 to 500 mJ/cm²). The laser beamconverged into a linear shape and having a width of from 100 to 1000 μm,e.g. 400 μm is, is irradiated to the entire substrate face. At thistime, overlapping ratio of the linear laser beam is set to from 50 to90%.

Next, a gate insulating film 5007 covering the island-like semiconductorlayers 5003 to 5006 is formed. The gate insulating film 5007 is formedfrom an insulating film containing silicon and having a thickness offrom 40 to 150 nm by using the plasma CVD method or a sputtering method.In this embodiment, the gate insulating film 5007 is formed from asilicon nitride oxide film of 120 nm in thickness. However, the gateinsulating film is not limited to such a silicon nitride oxide film, butit may be an insulating film containing other and having a single layeror a laminated layer structure. For example, when a silicon oxide filmis used, TEOS (Tetraethyl Orthosilicate) and O₂ are mixed by the plasmaCVD method, the reaction pressure is set to 40 Pa, the substratetemperature is set to from 300 to 400° C., and the high frequency (13.56MHZ) power density is set to from 0.5 to 0.8 W/cm² for electricdischarge. Thus, the silicon oxide film can be formed by discharge. Thesilicon oxide film manufactured in this way can then obtain preferablecharacteristics as the gate insulating film by thermal annealing at from400 to 500° C.

A first conductive film 5008 and a second conductive film 5009 forforming a gate electrode are formed on the gate insulating film 5007. Inthis embodiment, the first conductive film 5008 having a thickness offrom 50 to 100 nm is formed from Ta, and the second conductive film 5009having a thickness of from 100 to 300 nm is formed from W.

The Ta film is formed by a sputtering method, and the target of Ta issputtered by Ar. In this case, when suitable amounts of Xe and Kr areadded to Ar, internal stress of the Ta film is released, and pealing offthis film can be prevented. Resistivity of the Ta film of a phase isabout 20 μΩcm, and this Ta film can be used for the gate electrode.However, resistivity of the Ta film of β phase is about 180 μΩcm, and isnot suitable for the gate electrode. When tantalum nitride having acrystal structure close to that of the α phase of Ta and having athickness of about 10 to 50 nm is formed in advance as the base for theTa film to form the Ta film of the α phase, the Ta film of a phase canbe easily obtained.

The W film is formed by the sputtering method with W as a target.Further, the W film can be also formed by a thermal CVD method usingtungsten hexafluoride (WF₆). In any case, it is necessary to reduceresistance to use this film as the gate electrode. It is desirable toset resistivity of the W film to be equal to or smaller than 20 μΩcm.When crystal grains of the W film are increased in size, resistivity ofthe W film can be reduced. However, when there are many impurityelements such as oxygen, etc. within the W film, crystallization isprevented and resistivity is increased. Accordingly, in the case of thesputtering method, a W-target of 99.9999% or 99.99% in purity is used,and the W film is formed by taking a sufficient care of not mixingimpurities from a gaseous phase into the W film when the film is to beformed. Thus, a resistivity of from 9 to 20 μΩcm can be realized.

In this embodiment, the first conductive film 5008 is formed from Ta,and the second conductive film 5009 is formed from W. However, thepresent invention is not limited to this case. Each of these conductivefilms may also be formed from an element selected from Ta, W, Ti, Mo, Aland Cu, or an alloy material or a compound material having theseelements as principal components. Further, a semiconductor filmrepresented by a poly crystal silicon film doped with an impurityelement such as phosphorus may also be used. Examples of combinationsother than those shown in this embodiment include: a combination inwhich the first conductive film 5008 is formed from tantalum nitride(TaN), and the second conductive film 5009 is formed from W; acombination in which the first conductive film 5008 is formed fromtantalum nitride (TaN), and the second conductive film 5009 is formedfrom Al; and a combination in which the first conductive film 5008 isformed from tantalum nitride (TaN), and the second conductive film 5009is formed from Cu.

Next, a mask 5010 is formed from a resist, and first etching processingfor forming an electrode and wiring is performed. In this embodiment, anICP (Inductively Coupled Plasma) etching method is used, and CF₄ and Cl₂are mixed with a gas for etching. RF (13.56 MHZ) power of 500 W isapplied to the electrode of coil type at a pressure of 1 Pa so thatplasma is generated. RF (13.56 MHZ) of 100 W power is also applied to asubstrate side (sample stage), and a substantially negative self biasvoltage is applied. When CF₄ and Cl₂ are mixed, the W film and the Tafilm are etched to the same extent.

Under the above etching condition, end portions of a first conductivelayer and a second conductive layer are formed into a tapered shape byeffects of the bias voltage applied to the substrate side by making theshape of the mask formed from the resist into an appropriate shape. Theangle of a taper portion is set to from 15° to 45°. It is preferable toincrease an etching time by a ratio of about 10 to 20% so as to performthe etching without leaving the residue on the gate insulating film.Since a selection ratio of a silicon nitride oxide film to the W filmranges from 2 to 4 (typically 3), an exposed face of the silicon nitrideoxide film is etched by about 20 to 50 nm by over-etching processing.Thus, conductive layers 5011 to 5016 of a first shape (first conductivelayers 5011 a to 5016 a and second conductive layers 5011 b to 5016 b)formed of the first and second conductive layers are formed by the firstetching processing. A region that is not covered with the conductivelayers 5011 to 5016 of the first shape is etched by about 20 to 50 nm inthe gate insulating film 5007, so that a thinned region is formed. (SeeFIG. 10A).

Then, an impurity element for giving an n-type conductivity is added byperforming first doping processing. A doping method may be either an iondoping method or an ion implantation method. The ion doping method iscarried out under the condition that a dose is set to from 1×10¹³ to5×10¹⁴ atoms/cm², and an acceleration voltage is set to from 60 to 100keV. An element belonging to group 15, typically, phosphorus (P) orarsenic (As) is used as the impurity element for giving the n-typeconductivity. However, phosphorus (P) is used here. In this case, theconductive layers 5011 to 5015 serve as masks with respect to theimpurity element for giving the n-type conductivity, and first impurityregions 5017 to 5025 are formed in a self-aligning manner. The impurityelement for giving the n-type conductivity is added to the firstimpurity regions 5017 to 5025 in a concentration range from 1×10²⁰ to1×10²¹ atoms/cm³. (See FIG. 10B).

Second etching processing is next performed without removing the resistmask as shown in FIG. 10C. A W film is etched selectively by using CF₄,Cl₂ and O₂. The conductive layers 5026 to 5031 of a second shape (firstconductive layers 5026 a to 5031 a and second conductive layers 5026 bto 5031 b) are formed by the second etching processing. A region of thegate insulating film 5007, which is not covered with the conductivelayers 5026 to 5031 of the second shape, is further etched by about 20to 50 nm so that a thinned region is formed.

An etching reaction in the etching of the W film using the mixed gas ofCF₄ and Cl₂ and the Ta film can be assumed from the vapor pressure of aradical or ion species generated and a reaction product. When the vaporpressures of a fluoride and a chloride of W and Ta are compared, thevapor pressure of WF₆ as a fluoride of W is extremely high, and vaporpressures of other WCl₅, TaF₅ and TaCl₅ are approximately equal to eachother. Accordingly, both the W film and the Ta film are etched using themixed gas of CF₄ and Cl₂. However, when a suitable amount of O₂ is addedto this mixed gas, CF₄ and O₂ react and become CO and F so that a largeamount of F-radicals or F-ions is generated. As a is result, the etchingspeed of the W film whose fluoride has a high vapor pressure isincreased. In contrast to this, the increase in etching speed isrelatively small for the Ta film when F is increased. Since Ta is easilyoxidized in comparison with W, the surface of the Ta film is oxidized byadding O₂. Since no oxide of Ta reacts with fluorine or chloride, theetching speed of the Ta film is further reduced. Accordingly, it ispossible to make a difference in etching speed between the W film andthe Ta film so that the etching speed of the W film can be set to behigher than that of the Ta film.

As shown in FIG. 11A, second doping processing is then performed. Inthis case, an impurity element for giving the n-type conductivity isdoped in a smaller dose than in the first doping processing and at ahigh acceleration voltage by reducing a dose lower than that in thefirst doping processing. For example, the acceleration voltage is set tofrom 70 to 120 keV, and the dose is set to 1×10¹³ atoms/cm². Thus, a newimpurity region is formed inside the first impurity region formed in theisland-like semiconductor layer in FIG. 10B. In the doping, theconductive layers 5026 to 5030 of the second shape are used as maskswith respect to the impurity element, and the doping is performed suchthat the impurity element is also added to regions underside the firstconductive layers 5026 a to 5030 a. Thus, third impurity regions 5032 to5041 are formed. The third impurity regions 5032 to 5036 containphosphorus (P) with a gentle concentration gradient that conforms withthe thickness gradient in the tapered portions of the first conductivelayers 5026 a to 5030 a. In the semiconductor layers that overlap thetapered portions of the first conductive layers 5026 a to 5030 a, theimpurity concentration is slightly lower around the center than at theedges of the tapered portions of the first conductive layers 5026 a to5030 a. However, the difference is very slight and almost the sameimpurity concentration is kept throughout the semiconductor layers.

Third etching treatment is then carried out as shown in FIG. 11B. CHF₆is used as etching gas, and reactive ion etching (RIE) is employed.Through the third etching treatment, the tapered portions of the firstconductive layers 5026 a to 5031 a are partially etched to reduce theregions where the first conductive layers overlap the semiconductorlayers. Thus formed are third shape conductive layers 5037 to 5042(first conductive layers 5037 a to 5042 a and second conductive layers5037 b to 5042 b). At this point, regions of the gate insulating film5007 that are not covered with the third shape conductive layers 5037 to5042 are further etched and thinned by about 20 to 50 nm.

Third impurity regions 5032 to 5036 are formed through the third etchingtreatment. The third impurity regions 5032 a to 5036 a that overlap thefirst conductive layers 5037 a to 5041 a, respectively, and secondimpurity regions 5032 b to 5036 b each formed between a first impurityregion and a third impurity region.

As shown in FIG. 11C, fourth impurity regions 5043 to 5054 having theopposite conductivity type to the first conductivity type are formed inthe island-like semiconductor layers 5004 and 5006 for forming p-channelTFTs. The third shape conductive layers 5038 b and 5041 b are used asmasks against the impurity element and impurity regions are formed in aself-aligning manner. At this point, the island-like semiconductorlayers 5003 and 5005 for forming n-channel TFTs and the wiring portion5042 are entirely covered with a resist mask 5200. The impurity regions5043 to 5054 have already been doped with phosphorus in differentconcentrations. The impurity regions 5043 to 5054 are doped withdiborane (B₂H₆) through ion doping such that diborane dominatesphosphorus in each region and each region contain the impurity elementin a concentration of 2×10²⁰ to 2×10²¹ atoms/cm³.

Through the steps above, the impurity regions are formed in therespective island-like semiconductor layers. The third shape conductivelayers 5037 to 5041 overlapping the island-like semiconductor layersfunction as gate electrodes. Reference numeral 5042 function asisland-like source signal line.

After resist mask 5200 is removed, a step of activating the impurityelements added to the island-like semiconductor layers is performed tocontrol the conductivity type. This process is performed by a thermalannealing method using a furnace for furnace annealing. Further, a laserannealing method or a rapid thermal annealing method (RTA method) can beapplied. In the thermal annealing method, this process is performed at atemperature of from 400 to 700° C., typically from 500 to 600° C. withina nitrogen atmosphere in which oxygen concentration is equal to orsmaller than 1 ppm and is preferably equal to or smaller than 0.1 ppm.In this embodiment, heat treatment is performed for four hours at atemperature of 500° C. When a wiring material used in the third shapeconductive layers 5037 to 5042 is weak against heat, it is preferable toperform activation after an interlayer insulating film (having siliconas a principal component) is formed in order to protect wiring, etc.Further, the heat treatment is performed for 1 to 12 hours at atemperature of from 300 to 450° C. within an atmosphere including 3 to100% of hydrogen so that the island-like semiconductor layer ishydrogenerated. This step is to terminate a dangling bond of thesemiconductor layer by hydrogen thermally excited. Plasma hydrogenation(using hydrogen excited by plasma) may also be performed as anothermeasure for hydrogenation.

Next, as shown in FIG. 12A, a first interlayer insulating film 5055 isformed from a nitride oxide silicon film to 100 to 200 nm thick. Thesecond interlayer insulating film 5056 from an organic insulatingmaterial is formed on the first interlayer insulating film. Thereafter,contact holes are formed through the first interlayer insulating film5055, the second interlayer insulating film 5056 and the gate insulatingfilm 5007. Each wiring (including a connecting wiring and a signal line)5057 to 5062, and 5064 are patterned and formed. Thereafter, a pixelelectrode 5063 coming in contact with the connecting wiring 5062 ispatterned and formed.

A film having an organic resin as a material is used as the secondinterlayer insulating film 5056. Polyimide, polyamide, acrylic, BCB(benzocyclobutene), etc. can be used as this organic resin. Inparticular, since the second interlayer insulating film 5056 is providedmainly for planarization, acrylic excellent in leveling the film ispreferable. In this embodiment, an acrylic film having a thickness thatcan sufficiently level a level difference caused by the TFT is formed.The film thickness thereof is preferably set to from 1 to 5 μm (isfurther preferably set to from 2 to 4 μm).

In the formation of the contact holes, contact holes reaching n-typeimpurity regions 5017, 5018, 5021 and 5023 or p-type impurity regions5043 to 5054, a contact hole reaching wiring 5042, an contact holereaching an electric current supply line (not illustrated), and contactholes reaching gate electrodes (not illustrated) are formed.

Further, a laminate film of a three-layer structure is patterned in adesired shape and is used as wiring (including a connecting wiring andsignal line) 5057 to 5062, 5064. In this three-layer structure, a Tifilm of 100 [nm] in thickness, a Ti-containing aluminum film of 300 [nm]in thickness, and a Ti film of 150 [nm] in thickness are continuouslyformed by the sputtering method. However, another conductive film mayalso be used.

In this embodiment, an ITO film of 110 nm in thickness is formed as apixel electrode 5063, and is patterned. Contact is made by arranging thepixel electrode 5063 such that this pixel electrode 5063 comes incontact with the connecting electrode 5062 and is overlapped with thisconnecting wiring 5062. Further, a transparent conductive film providedby mixing 2 to 20% of zinc oxide (ZnO) with indium oxide may also beused. This pixel electrode 5063 becomes an anode of the OLED. (See FIG.12A).

As shown in FIG. 12B, an insulating film (a silicon oxide film in thisembodiment) containing silicon and having a thickness of 500 nm is nextformed. A third interlayer insulating film 5065 is formed in which anopening is formed in a position corresponding to the pixel electrode5063. When the opening is formed, a side wall of the opening can easilybe tapered by using the wet etching method. When the side wall of theopening is not gentle enough, deterioration of an organic light emittinglayer caused by a level difference becomes a notable problem.

Next, an organic light emitting layer 5066 and a cathode (MgAgelectrode) 5067 are continuously formed by using the vacuum evaporationmethod without exposing to the atmosphere. The organic light emittinglayer 5066 has a thickness of from 80 to 200 nm (typically from 100 to120 nm), and the cathode 5067 has a thickness of from 180 to 300 nm(typically from 200 to 250 nm).

In this process, the organic light emitting layer is sequentially formedwith respect to a pixel corresponding to red, a pixel corresponding togreen and a pixel corresponding to blue. In this case, since the organiclight emitting layer has an insufficient resistance against a solution,the organic light emitting layer must be formed separately for eachcolor instead of using a photolithography technique. Therefore, it ispreferable to cover a portion except for desired pixels using a metalmask so that the organic light emitting layer is formed selectively onlyin a required portion.

Namely, a mask for covering all portions except for the pixelcorresponding to red is first set, and the organic light emitting layerfor emitting red light are selectively formed by using this mask. Next,a mask for covering all portions except for the pixel corresponding togreen is set, and the organic light emitting layer for emitting greenlight are selectively formed by using this mask. Next, a mask forcovering all portions except for the pixel corresponding to blue issimilarly set, and the organic light emitting layer for emitting bluelight are selectively formed by using this mask. Here, different masksare used, but instead the same single mask may be used repeatedly.

Here, a system for forming three kinds of OLED corresponding to RGB isused. However, a system in which an OLED for emitting white light and acolor filter are combined, a system in which the OLED for emitting blueor blue green light is combined with a fluorescent substance (afluorescent color converting layer: CCM), a system for overlapping theOLED respectively corresponding to R, G, and B with the cathodes(opposite electrodes) by utilizing a transparent electrode, etc. may beused.

A known material can be used as the organic light emitting layer 5066.An organic material is preferably used as the known material inconsideration of a driving voltage. For example, a four-layer structureconsisting of a hole injection layer, a hole transportation layer, alight emitting layer and an electron injection layer is preferably usedfor the organic light emitting layer.

The cathode 5067 is formed next on the pixel (pixel on the same line)included the switching TFT in which the gate electrode is connected tothe same gate signal line by using a metal mask. This embodiment usesMgAg for the cathode 5067 but it is not limited thereto. Other knownmaterials may be used for the cathode 5067.

Finally, a planarization film 5068 formed of a silicon nitride film andhaving a thickness of 300 nm is formed. In reality, the planarizationfilm 5068 plays a role of protecting the organic light emitting layer5066 from moisture, etc. However, reliability of OLED can be furtherimproved by forming the planarization film 5068.

Thus, the state as shown in FIG. 12B is completed. Though not shown infigures, according to manufacturing method in Embodiment Mode 1, thesecond substrate providing sealing film is bonded to the planarizationfilm 5068 by using a second bonding layer. In addition, following stepscan be executed in according to methods shown in Embodiment Mode 1. Inaccordance of manufacturing method in Embodiment Mode 2, the secondsubstrate providing sealing film is bonded to the planarization film5068 by using a second bonding layer. In addition, following steps canbe executed in according to methods shown in Embodiment Mode 2.

In the process of forming the light emitting device in this embodiment,the source signal line is formed from Ta and W that are materials of thegate electrodes, and the gate signal line is formed from Al that is awiring material of the source and drain electrodes for conveniences ofthe circuit construction and procedures in the process. However,different materials may also be used.

The light emitting device in this embodiment has very high reliabilityand improved operating characteristics by arranging the TFTs of theoptimal structures in a driving circuit portion in addition to the pixelportion. Further, in a crystallization process, crystallinity can bealso improved by adding a metal catalyst such as Ni. Thus, a drivingfrequency of the source signal line driving circuit can be set to 10 MHzor more.

First, the TFT having a structure for reducing hot carrier injection soas not to reduce an operating speed as much as possible is used as ann-channel type TFT of a CMOS circuit forming the driving circuitportion. Here, the driving circuit includes a shift register, a buffer,a level shifter, a latch in line sequential driving, a transmission gatein dot sequential driving, etc.

In the case of this embodiment, an active layer of the n-channel typeTFT includes a source region, a drain region, an overlap LDD region (Lovregion) that is overlapped with the gate electrode through the gateinsulating film, an offset LDD region (Loff region) that is notoverlapped with the gate electrode through the gate insulating film, andchannel formation region.

Deterioration by the hot carrier injection in the p-channel type TFT ofthe CMOS circuit is almost neglectible. Therefore, it is not necessaryto particularly form the LDD region in this n-channel type TFT. However,similar to the n-channel type TFT, the LDD region can be formed as a hotcarrier countermeasure.

Further, when the CMOS circuit for bi-directionally flowing an electriccurrent through a channel forming region, i.e., the CMOS circuit inwhich roles of the source and drain regions are exchanged is used in thedriving circuit, it is preferable for the n-channel type TFT thatconstitutes the CMOS circuit to form LDD regions such that the channelforming region is sandwiched between the LDD regions. As an example ofthis, a transmission gate used in the dot sequential driving is given.When a CMOS circuit required to reduce an OFF-state current value asmuch as possible is used in the driving circuit, the n-channel type TFTforming the CMOS circuit preferably has a Lov region. The transmissiongate used in the dot sequential driving can be given also as an exampleas such.

In reality, when the light emitting device is completed according toEmbodiment Modes 1 or 2, it is preferable to perform packaging (sealing)using a protective film (a laminate film, an ultraviolet curable resinfilm, etc.) that has a high airtight seal property and allows littledegasification and a translucent sealing member in order to prevent tobe exposed to the outside air. In this case, reliability of OLED isimproved by filling the interior of the sealing member with an inert gasatmosphere and arranging a moisture absorbing material (e.g., bariumoxide) therein.

Further, after the airtight seal property is improved by processing ofpackaging, etc., a connector (flexible printed circuit: FPC) is attachedto complete the device as a product. The connector is for connecting,with an external signal terminal, a terminal led out from the element orthe circuit which is formed on the substrate. The device in this stateis ready to be shipped and is called a self-emission device in thisspecification.

Furthermore, in accordance with the processes shown in this embodiment,the number of photomasks can be reduced that is need for manufacturingthe light emitting device. As a result, the processes can be reduced,and this contributes to a reduction in the manufacturing costs and anincrease in throughput.

Note that it is possible to implement Embodiment 3 in combination withEmbodiments 1 to 2.

Embodiment 4

In Embodiment 4, a structure of a light emitting device usinginverse-stagger type TFTs according to the present invention will bedescribed.

FIG. 13 is a cross-sectional view showing a light emitting deviceaccording to the present invention. A sealing film 601 is formed on aflexible third substrate 601. The sealing film 601 includes a barrierfilm 601 a, a stress relaxing film 601 b and a barrier film 601 c.

A sealing film 608 is formed on a flexible second substrate 606. Thesealing film 608 includes a barrier film 608 a, a stress relaxing film608 b and a barrier film 608 c.

Between the sealing films 601 and 608, TFTs, an OLED and other elementsare formed. In this embodiment, a TFT 604 a included in a drivingcircuit 610 and TFTs 604 b and 604 c included in a pixel portion 611 areshown as representative examples.

An OLED 605 includes a pixel electrode 640, an organic light emittinglayer 641 and a cathode 642.

The TFT 604 a includes gate electrodes 613 and 614, an insulating film612 formed so as to be in contact with the gate electrodes 613 and 614,and a semiconductor film 615 formed so as to be in contact with theinsulating film 612. The TFT 604 b includes gate electrodes 620 and 621,the insulating film 612 formed so as to be in contact with the gateelectrodes 620 and 621, and a semiconductor film 622 formed so as to bein contact with the insulating film 612. The TFT 604 c includes a gateelectrode 630, the insulating film 612 formed so as to be in contactwith the gate electrode 630, and a semiconductor film 631 formed so asto be in contact with the insulating film 612.

Although there is shown the example where the inverse-stagger type TFTsare used in the light emitting device manufactured according toEmbodiment mode 1, the structure of the present invention is not limitedthereto. The inverse-stagger type TFTs may be used in the light emittingdevice manufactured according to Embodiment mode 2.

Embodiment 4 can be carried out in free combination with Embodiment 1.

Embodiment 5

In Embodiment 5, an example where a bonding layer is removed by sprayinga fluid thereon will be described.

As a method of spraying a fluid, a method of spraying a high-pressurewater flow from a nozzle on an object (referred to as a water jetmethod) or a method of spraying a high-pressure gas flow on an objectcan be used. In the case of the water jet method, an organic solvent, anacid solution or an alkaline solution may be used instead of water. As agas flow, air, a nitrogen gas, a carbon dioxide gas or a rare gas may beused. Furthermore, a plasma obtained from these gases may also be used.It is important to select an appropriate fluid in accordance with amaterial of the bonding layer and materials of the films and substrateswhich are not desired to be removed so that such films and substratesare not removed with removal of the bonding layer.

As a bonding layer, a porous silicon layer or a silicon layer to whichhydrogen, oxygen, nitrogen or a rare gas is added is used. In the casewhere a porous silicon layer is used, an amorphous silicon film or apolycrystalline silicon film may be subjected to anodization to provideporousness thereto for use.

FIG. 14 shows removal of a bonding layer by a water jet method. An OLED604 is provided between substrates 603 and 606. The OLED 604 is coveredwith an insulating film 603. A sealing film 609 including a plurality ofinsulating films is provided between the insulating film 603 and thesubstrate 606.

An insulating film 605 and a bonding layer 606 are provided between thesubstrate 603 and the OLED 604. The bonding layer 606 is in contact withthe substrate 603. Although only the OLED is representatively shown inFIG. 14, TFTs and other elements are normally provided between theinsulating films 605 and 603.

The bonding layer 606 may have a thickness of 0.1 to 900 μm (preferably,0.5 to 10 μm). In Embodiment 5, an SOG film having a thickness of 1 μmis used as the bonding layer 606.

A fluid 607 is sprayed from a nozzle 608 onto the bonding layer 606. Inorder to efficiently spray the fluid 607 onto the entire exposed portionof the bonding layer 606, it is recommended to spray the fluid whilerotating the bonding layer 606 around a central line perpendicular tothe substrate 601, as is indicated with an arrow in FIG. 14. The fluid607, to which a pressure of 1×10⁷ to 1×10⁹ Pa (preferably, 3×10⁷ to5×10⁸ Pa) is applied, is sprayed from the nozzle 608 onto the exposedportion of the bonding layer 606. Since the sample rotates, the fluid607 is sprayed along the exposed surface of the bonding layer 606.

When the fluid emitted from the nozzle 608 is sprayed onto the bondinglayer 606, the bonding layer is broken due to impact for its fragilityand then is removed or is chemically removed. As a result, the bondinglayer 606 is broken or removed to separate the substrate 603 and theinsulating film 605 from each other. In the case where the separation isachieved by breaking the bonding layer 606, the remaining bonding layermay be removed by etching.

As the fluid 607, a liquid such as water, an organic solvent, an acidsolution or an alkaline solution may be used. Alternatively, air, anitrogen gas, a carbon dioxide gas or a rare gas may be also used.Furthermore, a plasma obtained from these gases may be used.

Embodiment 5 can be carried out in combination with Embodiments 1 to 4.

Embodiment 6

In this embodiment, an external light emitting quantum efficiency can beremarkably improved by using an organic light emitting material by whichphosphorescence from a triplet exciton can be employed for emitting alight. As a result, the power consumption of OLED can be reduced, thelifetime of OLED can be elongated and the weight of OLED can belightened.

The following is a report where the external light emitting quantumefficiency is improved by using the triplet exciton (T. Tsutsui, C.Adachi, S. Saito, Photochemical Processes in Organized MolecularSystems, ed. K. Honda, (Elsevier Sci. Pub., Tokyo, 1991) p. 437).

The molecular formula of an organic light emitting material (coumarinpigment) reported by the above article is represented as follows.

-   -   (M. A. Baldo, D. F. O'Brien, Y. You, A. Shoustikov, S.        Sibley, M. E. Thompson, S. R. Forrest, Nature 395 (1998) p. 151)

The molecular formula of an EL material (Pt complex) reported by theabove article is represented as follows.

(M. A. Baldo, S. Lamansky, P. E. Burrows, M. E. Thompson, S. R. Forrest,Appl. Phys. Lett., 75 (1999) p. 4.) (T. Tsutsui, M.-J. Yang, M. Yahiro,K. Nakamura, T. Watanabe. T. Tsuji, Y. Fukuda, T. Wakimoto, S.Mayaguchi, Jpn, Appl. Phys., 38 (12B) (1999) L1502).

The molecular formula of an EL material (Ir complex) reported by theabove article is represented as follows.

As described above, if phosphorescence from a triplet exciton can be putto practical use, it can realize the external light emitting quantumefficiency three to four times as high as that in the case of usingfluorescence from a singlet exciton in principle.

The structure according to this embodiment can be freely implemented incombination of any structures of the Embodiments 1 to 5.

Embodiment 7

A film made of an organic light emitting material is generally formed byan ink jet method, a spin-coating method or an evaporation method. InEmbodiment 7, a method for forming an organic light emitting layer otherthan the above-mentioned methods will be described.

In this embodiment, a film containing molecular assemblies of an organiclight emitting material is formed on a substrate under an inert gasatmosphere by spraying, using a colloidal solution in which molecularassemblies constituting the organic light emitting material aredispersed (also referred to as a sol). The organic light emittingmaterial is present as particles, each being an assembly of severalmolecules in a liquid.

FIG. 15 shows the formation of an organic light emitting layer 650 byspraying a composition from a nozzle (not shown) in an inert gas (inthis embodiment, a nitrogen gas). The composition is obtained bydispersing tris(2-phenylpyridine) iridium (Ir(ppy)₃) which is an iridiumcomplex serving as an organic light emitting material, andbathocupuroine (BCP) which is an organic light emitting material servingas a host (hereinafter, referred to as a host material) in toluene.

In FIG. 15, the organic light emitting layer 650 is selectively formedto have a thickness of 25 to 40 nm by using a mask 651. Both the iridiumcomplex and BCP are insoluble to toluene.

In practice, there are some cases where the organic light emitting layeris used in a single-layered form and the other cases where it is used ina multi-layered form. In the case where the organic light emitting layerhas a multi-layered structure, another (other) organic light emittinglayer(s) is (are) formed in a similar manner after formation of theorganic light emitting layer 650. In this case, all the depositedorganic light emitting layers are collectively referred to as theorganic light emitting layer.

A film formation method of this embodiment allows the formation of afilm even if the organic light emitting material in a liquid is in anystate. Particularly, this method permits an organic light emitting layerwith good quality to be formed by using an organic light emittingmaterial that is hardly dissolved. Moreover, since a film is formed byspraying a liquid containing an organic light emitting material with useof a carrier gas, the film formation can be achieved within a shortperiod of time. A method of producing a liquid containing an organiclight emitting material to be sprayed can be extremely simplified.Furthermore, in this embodiment, a mask is used to form a film having adesired pattern, so that the film formation is conducted through anopening of the mask. In addition, in order to efficiently use anexpensive organic light emitting material, it is possible to collect theorganic light emitting material adhered to the mask for reuse.

The ink jet method and the spin-coating method have a restriction inthat an organic light emitting material having a high solubility to asolvent cannot be used. The evaporation has a restriction in that anorganic light emitting material which decomposes before evaporationcannot be used. However, the film formation method of this embodiment isnot affected by the above-mentioned restrictions.

As examples of the organic light emitting material suitable for the filmformation method of this embodiment, quinacridon, tris(2-phenylpyridine)iridium, bathocuproine, poly(1,4-phenylenevinylene),poly(1,4-naphthalenevinylene), poly(2-phenyl-1,4-phenylenevinylene),polythiophene, poly(3-phenylthiophene), poly(1,4-phenylene),poly(2,7-fluorene) and the like can be given.

The structure of Embodiment 7 can be carried out in free combinationwith any of Embodiments 1 to 6.

Embodiment 8

This embodiment gives descriptions that are more detailed of the pixelportion of the light emitting device obtained by the present inventionin Embodiment 8. The top structure of the pixel portion is shown in FIG.16A whereas the circuit diagram thereof is shown in FIG. 16B. Commonreference symbols are used in FIG. 16A and FIG. 16B to becross-referred.

A switching TFT 802 has a source connected to a source wiring 815 andhas a drain connected to a drain wiring 805. The drain wiring 805 iselectrically connected to a gate electrode 807 of a current controllingTFT 806. The current controlling TFT 806 has a source electricallyconnected to a current supply line 816 and has a drain electricallyconnected to a drain wiring 817. The drain wiring 817 is electricallyconnected to a pixel electrode (cathode) 818 indicated by the dottedline.

A capacitor storage is formed here in a region denoted by 819. Thecapacitor storage 819 is composed of a semiconductor film 820 that iselectrically connected to the current supply line 816, an insulatingfilm (not shown) on the same layer as the gate insulating film, and thegate electrode 807. A capacitor composed of the gate electrode 807, thesame layer (not shown) as the first interlayer insulating film, and thecurrent supply line 816 may also be used as a storage capacitor.

This embodiment 8 can be combined with Embodiments 1 to 7.

Embodiment 9

This embodiment shows an example of the circuit structure of the lightemitting device with reference to FIG. 17. The circuit structure shownin this embodiment is for digital driving. The structure according tothis embodiment has a source side driver circuit 901, a pixel portion906 and a gate side driver circuit 907.

The source side driver circuit 901 is provided with a shift register902, a latch (A) 903, a latch (B) 904, and a buffer 905. In the case ofanalog driving, a sampling circuit (transfer gate) is provided in placeof the latches (A) and (B). The gate side driver circuit 907 is providedwith a shift register 908 and a buffer 909. However, the buffer 909 isnot always necessary to provide.

In this embodiment, the pixel portion 906 includes a plurality ofpixels, each of which is provided with OLED. It is preferable that acathode of OLED is electrically connected to a drain of a currentcontrolling TFT.

The source side driver circuit 901 and the gate side driver circuit 907are composed of n-channel TFTs or p-channel TFTs obtained in accordancewith Embodiments 2 to 4.

Though not shown, another gate side driver circuit may be added oppositethe gate side driver circuit 907 across the pixel portion 906. In thiscase, two of the gate side driver circuits have the same structure andshare a gate wiring, so that the other can send a gate signal in placeof the broken one to make the pixel portion operate normally.

This embodiment can be combined with Embodiments 1 to 8.

Embodiment 10

In Embodiment 10, a roll-to-roll method of forming a sealing film on aflexible plastic substrate will be described.

FIG. 19 shows a structure of a film formation apparatus according toEmbodiment 10 in a simplified manner. The film formation apparatusaccording to the present invention shown in FIG. 19 includes twochambers 804 and 809 for forming a barrier film by sputtering, chambers805 to 808 for controlling an air pressure within the chambers 804 and809, a mechanism 820 for applying a resin, and a mechanism 813 forcuring an applied resin.

The chamber 804 for forming a barrier film by sputtering includes a roll801 for unwinding a substrate 802, a voltage application electrode 810having a target, and a heater 811 also serving as an electrode. Thechamber 809 for forming a barrier film by sputtering is includes a roll803 for winding the substrate 802, a voltage application electrode 814having a target, and a heater 815 also serving as an electrode.

The substrate 802 is carried from the unwinding roll 801 to the windingroll 803.

In this embodiment, a silicon nitride film is formed in the chamber 804.More specifically, an air pressure within the chamber 804 is kept to 0.4Pa by a turbo-molecular pump or the like. In this state, argon at a flowrate of 10 sccm, nitrogen at 35 sccm and hydrogen at 5 sccm aresupplied.

The substrate 802, on which a silicon nitride film is formed in thechamber 804, successively passes through the chambers 805 and 806, andthen is placed under the atmospheric pressure. A resin 812 is appliedonto the substrate 802 by the mechanism 820 for applying a resin. Thechambers 805 and 806 are both evacuated to a vacuum by a turbo-molecularpump or the like, and are provided so as to keep an air pressure withinthe chamber 804 to a desired level without being affected by theatmospheric pressure. Although the two chambers 805 and 806 are used toprevent the influence of the atmospheric pressure, only one chamber maybe sufficient depending on the case. It is possible to provide three ormore chambers as the need arises.

As the resin 812, thermally polymerizable polyethylene is used in thisembodiment. After application of the resin 812, the substrate 802 isheated with a halogen lamp 813 so as to cure the applied resin 812.

More specifically, in this embodiment, a halogen lamp for heating thesubstrate is provided as the mechanism 813 for curing the applied resin.In the case where the resin is to be cured by heating, means of heatingis not limited to a halogen lamp; an infrared lamp, a metal halide lamp,a xenon arc lamp, a carbon arc lamp, a high-pressure sodium lamp or ahigh-pressure mercury lamp can be also used. Moreover, means of heatingis not limited to a lamp; heating may be performed by using a heater orthe like. In the case where the resin is not thermally curable butultraviolet curable, the resin can be cured by radiation of anultraviolet ray.

The substrate 802, on which the resin film is formed, is delivered tothe chambers 807 and 808 to finally reach the chamber 809. The chambers807 and 808 are both evacuated to a vacuum by a turbo-molecular pump orthe like, and are provided so as to keep an air pressure within thechamber 809 to a desired level without being affected by the atmosphericpressure. Although two chambers 807 and 808 are used to prevent theinfluence of the atmospheric pressure, only one chamber may besufficient depending on the case. It is possible to provide three ormore chambers as the need arises.

A silicon oxynitride film is formed in the chamber 809. Morespecifically, while keeping an air pressure within the chamber 809 to0.4 Pa by a turbo-molecular pump or the like, argon at a flow rate of 10sccm, nitrogen at 31 sccm, hydrogen at 5 sccm and N₂O at 4 sccm aresupplied.

The substrate 802, on which the silicon oxynitride film is formed, isrewound by the winding roll 803.

The above-described structure facilitates the mass production of theflexible plastic substrate which has a sealing film including a stressrelaxing film interposed between two barrier films.

Although the film formation apparatus for forming the sealing filmincluding a laminate of a silicon nitride film, a film made ofpolyethylene, and a silicon oxynitride film is described in thisembodiment, a material of the barrier film is not limited thereto. Inaddition, a material of the stress relaxing film is not limited topolyethylene; any resin material having a smaller stress than that ofthe barrier film may be used.

Although two barrier films are formed in this embodiment, three or morebarrier films may be formed. In such a case, it is sufficient to providea chamber for sputtering, a chamber for preventing the influence of theatmospheric pressure, a mechanism for applying a resin, and a mechanismfor curing the applied resin, in a manner suitable for each filmformation.

Moreover, a multi-layered sealing film including barrier films and astress relaxing film may be formed by repeating the step of rewindingthe wound substrate around the unwinding roll 801 after winding up thesubstrate 802 around the winding roll 803.

Embodiment 10 may be combined with any of Embodiments 1 to 9.

Embodiment 11

Being self-luminous, a light emitting device using a light emittingelement has better visibility in bright places and wider viewing anglethan liquid crystal display devices. Therefore, the light emittingdevice can be used to the display device of various electric appliances.

Given as examples of an electric appliance that employs a light emittingdevice manufactured in accordance with the present invention are videocameras, digital cameras, goggle type displays (head mounted displays),navigation systems, audio reproducing devices (such as car audio andaudio components), notebook computers, game machines, portableinformation terminals (such as mobile computers, cellular phones,portable game machines, and electronic books), and image reproducingdevices equipped with recording media (specifically, devices with adisplay device that can reproduce data in a recording medium such as adigital video disk (DVD) to display an image of the data). Wide viewingangle is important particularly for portable information terminalsbecause their screens are often slanted when they are looked at.Therefore it is preferable for portable information terminals to employthe light emitting device using the light emitting element. Specificexamples of these electric appliance are shown in FIGS. 18A to 18H.

FIG. 18A shows a digital still camera, which is composed of a main body2101, a display unit 2102, an image receiving unit 2103, operation keys2104, an external connection port 2105, a shutter 2106, etc. The lightemitting device manufactured in accordance with the present inventioncan be applied to the display unit 2102.

FIG. 18B shows a mobile computer, which is composed of a main body 2301,a display unit 2302, a switch 2303, operation keys 2304, an infraredport 2305, etc. The light emitting device manufactured in accordancewith the present invention can be applied to the display unit 2302.

FIG. 18C shows a goggle type display (head mounted display), which iscomposed of a main body 2501, display units 2502, and arm units 2503.The light emitting device manufactured in accordance with the presentinvention can be applied to the display units 2502.

FIG. 18D shows a cellular phone, which is composed of a main body 2701,a case 2702, a display unit 2703, an audio input unit 2704, an audiooutput unit 2705, operation keys 2706, an external connection port 2707,an antenna 2708, etc. The light emitting device manufactured inaccordance with the present invention can be applied to the display unit2703. If the display unit 2703 displays white letters on blackbackground, the cellular phone consumes less power.

If the luminance of light emitted from organic materials is raised infuture, the light emitting device can be used in front or rearprojectors by enlarging outputted light that contains image informationthrough a lens or the like and projecting the light.

These electric appliances now display with increasing frequencyinformation sent through electronic communication lines such as theInternet and CATV (cable television), especially, animation information.Since organic materials have very fast response speed, the lightemitting device is suitable for animation display.

In the light emitting device, light emitting portions consume power andtherefore it is preferable to display information in a manner thatrequires less light emitting portions. When using the light emittingdevice in display units of portable information terminals, particularlycellular phones and audio reproducing devices that mainly display textinformation, it is preferable to drive the device such that non-lightemitting portions form a background and light emitting portions formtext information.

As described above, the application range of the light emitting devicemanufactured by using the deposition device of the present invention isso wide that it is applicable to electric appliances of any field. Theelectric appliances of this embodiment can employ any light emittingdevice shown in Embodiments 1 to 10.

According to the present invention, owing to a laminate structure of aplurality of barrier films, even if a crack occurs in one of the barrierfilms, the other barrier films can effectively prevent moisture oroxygen from penetrating into the organic light emitting layer.Furthermore, even if the quality of the barrier films is degraded due toa low film formation temperature, the laminate structure of a pluralityof barrier films can effectively prevent moisture or oxygen frompenetrating into the organic light emitting layer.

Furthermore, a stress relaxing film having a smaller stress than that ofthe barrier films is interposed between the barrier films, so that astress of the entire insulating films can be reduced. Thus, the barrierfilms sandwiching the stress relaxing film therebetween hardly suffer acrack due to stress as compared with a single-layered barrier film evenwhen the multi-layered barrier film has the same total thickness as thatof the single-layered barrier film.

Accordingly, the multi-layered barrier film can effectively preventmoisture or oxygen from penetrating into the organic light emittinglayer as compared with a single-layered barrier film even when themulti-layered barrier film has the same total thickness as that of thesingle-layered barrier film. Furthermore, a crack due to stress ishardly generated in such a multi-layered barrier film.

1. A camera comprising: a display unit, the display unit comprising: afirst substrate; a second substrate; a light emitting element formedbetween the first substrate and the second substrate; a plurality offirst insulating films formed between the first substrate and the lightemitting element; at least one second insulating film formed in eachspace between the plurality of first insulating films; a plurality ofthird insulating films formed between the second substrate and the lightemitting element; and at least one fourth insulating film formed in eachspace between the plurality of third insulating films, wherein the firstsubstrate and the second substrate are formed of plastic, and whereinthe at least one second insulating film has a smaller stress than thatof each of the plurality of first insulating films and the at least onefourth insulating film has a smaller stress than that of each of theplurality of third insulating films.
 2. A camera according to claim 1,wherein at least one of the first substrate and the second substrate hasflexibility.
 3. A camera according to claim 1, wherein the plasticcomprises any one selected from the group consisting of polyethersulfone, polycarbonate, polyethylene terephthalate and polyethylenenaphthalate.
 4. A camera according to claim 1, wherein at least one ofthe plurality of first insulating films and the plurality of thirdinsulating films comprises any one selected from the group consisting ofsilicon nitride, silicon oxynitride, aluminum oxide, aluminum nitride,aluminum oxynitride and aluminum silicide oxynitride.
 5. A cameraaccording to claim 1, wherein the second insulating film and the fourthinsulating film comprises any one selected from the group consisting ofpolyimide, acryl, polyamide, polyimide amide, benzocyclobutene and anepoxy resin.
 6. A camera comprising: a display unit, the display unitcomprising: a first substrate; a second substrate; a light emittingelement and a thin film transistor, formed between the first substrateand the second substrate; a plurality of first insulating films formedbetween the first substrate, and the light emitting element and the thinfilm transistor; at least one second insulating film formed in eachspace between the plurality of first insulating films; a plurality ofthird insulating films formed between the second substrate, and thelight emitting element and the thin film transistor; and at least onefourth insulating film formed in each space between the plurality ofthird insulating films, wherein the first substrate and the secondsubstrate are formed of plastic, and wherein the at least one secondinsulating film has a smaller stress than that of each of the pluralityof first insulating films; and the at least one fourth insulating filmhas a smaller stress than that of each of the plurality of thirdinsulating films.
 7. A camera according to claim 6, wherein at least oneof the first substrate and the second substrate has flexibility.
 8. Acamera according to claim 6, wherein the plastic comprises any oneselected from the group consisting of polyether sulfone, polycarbonate,polyethylene terephthalate and polyethylene naphthalate.
 9. A cameraaccording to claim 6, wherein at least one of the plurality of firstinsulating films and the plurality of third insulating films comprisesany one selected from the group consisting of silicon nitride, siliconoxynitride, aluminum oxide, aluminum nitride, aluminum oxynitride andaluminum silicide oxynitride.
 10. A camera according to claim 6, whereinat least one of the second insulating film and the fourth insulatingfilm comprises any one selected from the group consisting of polyimide,acryl, polyamide, polyimide amide, benzocyclobutene and an epoxy resin.11. A camera comprising: a display unit, the display unit comprising: asubstrate; a light emitting element; a plurality of first insulatingfilms formed between the substrate and the light emitting element; atleast one second insulating film formed in each space between theplurality of first insulating films; a plurality of third insulatingfilms; and at least one fourth insulating film formed in each spacebetween the plurality of third insulating films, wherein the lightemitting element is formed between the plurality of third insulatingfilms and the substrate, wherein the substrate is formed of plastic, andwherein the at least one second insulating film has a smaller stressthan that of each of the plurality of first insulating films and the atleast one fourth insulating film has a smaller stress than that of eachof the plurality of third insulating films.
 12. A camera according toclaim 11, wherein the substrate has flexibility.
 13. A camera accordingto claim 11, wherein the plastic comprises any one selected from thegroup consisting of polyether sulfone, polycarbonate, polyethyleneterephthalate and polyethylene naphthalate.
 14. A camera according toclaim 11, wherein at least one of the plurality of first insulatingfilms and the plurality of third insulating films comprises any oneselected from the group consisting of silicon nitride, siliconoxynitride, aluminum oxide, aluminum nitride, aluminum oxynitride andaluminum silicide oxynitride.
 15. A camera according to claim 11,wherein at least one of the second insulating film and the fourthinsulating film comprises any one selected from the group consisting ofpolyimide, acryl, polyamide, polyimide amide, benzocyclobutene and anepoxy resin.
 16. A camera comprising: a display unit, the display unitcomprising: a substrate; a light emitting element and a thin filmtransistor; a plurality of first insulating films formed between thesubstrate, and the light emitting element and the thin film transistor;at least one second insulating film formed in each space between theplurality of first insulating films; a plurality of third insulatingfilms; and at least one fourth insulating film formed in each spacebetween the plurality of third insulating films, wherein the lightemitting element and the thin film transistor are formed between theplurality of third insulating films and the substrate, wherein thesubstrate is formed of plastic, and wherein the at least one secondinsulating film has a smaller stress than that of each of the pluralityof first insulating films and the at least one fourth insulating filmhas a smaller stress than that of each of the plurality of thirdinsulating films.
 17. A camera according to claim 16, wherein thesubstrate has flexibility.
 18. A camera according to claim 16, whereinthe plastic comprises any one selected from the group consisting ofpolyether sulfone, polycarbonate, polyethylene terephthalate andpolyethylene naphthalate.
 19. A camera according to claim 16, wherein atleast one of the plurality of first insulating films and the pluralityof third insulating films comprises any one selected from the groupconsisting of silicon nitride, silicon oxynitride, aluminum oxide,aluminum nitride, aluminum oxynitride and aluminum silicide oxynitride.20. A camera according to claim 16, wherein at least one of the secondinsulating film and the fourth insulating film comprises any oneselected from the group consisting of polyimide, acryl, polyamide,polyimide amide, benzocyclobutene and an epoxy resin.
 21. A cameracomprising: a display unit, the display unit comprising: a firstsubstrate; a second substrate; a light emitting element formed betweenthe first substrate and the second substrate; a plurality of firstinsulating films formed between the first substrate and the lightemitting element; at least one second insulating film formed in eachspace between the plurality of first insulating films; a first bondinglayer formed between the first substrate and the plurality of firstinsulating films; a plurality of third insulating films formed betweenthe second substrate and the light emitting element; at least one fourthinsulating film formed in each space between the plurality of thirdinsulating films; and a second bonding layer formed between the secondsubstrate and the plurality of third insulating films, wherein the firstsubstrate and the second substrate are formed of plastic, and whereinthe at least one second insulating film has a smaller stress than thatof each of the plurality of first insulating films and the at least onefourth insulating film has a smaller stress than that of each of theplurality of third insulating films.
 22. A camera according to claim 21,wherein at least one of the first substrate and the second substrate hasflexibility.
 23. A camera according to claim 21, wherein the plasticcomprises any one selected from the group consisting of polyethersulfone, polycarbonate, polyethylene terephthalate and polyethylenenaphthalate.
 24. A camera according to claim 21, wherein at least one ofthe plurality of first insulating films and the plurality of thirdinsulating films comprises any one selected from the group consisting ofsilicon nitride, silicon oxynitride, aluminum oxide, aluminum nitride,aluminum oxynitride and aluminum silicide oxynitride.
 25. A cameraaccording to claim 21, wherein at least one of the second insulatingfilm and the fourth insulating film comprises any one selected from thegroup consisting of polyimide, acryl, polyamide, polyimide amide,benzocyclobutene and an epoxy resin.
 26. A computer comprising: adisplay unit, the display unit comprising: a first substrate; a secondsubstrate; a light emitting element formed between the first substrateand the second substrate; a plurality of first insulating films formedbetween the first substrate and the light emitting element; at least onesecond insulating film formed in each space between the plurality offirst insulating films; a plurality of third insulating films formedbetween the second substrate and the light emitting element; and atleast one fourth insulating film formed in each space between theplurality of third insulating films, wherein the first substrate and thesecond substrate are formed of plastic, and wherein the at least onesecond insulating film has a smaller stress than that of each of theplurality of first insulating films and the at least one fourthinsulating film has a smaller stress than that of each of the pluralityof third insulating films.
 27. A computer according to claim 26, whereinat least one of the first substrate and the second substrate hasflexibility.
 28. A computer according to claim 26, wherein the plasticcomprises any one selected from the group consisting of polyethersulfone, polycarbonate, polyethylene terephthalate and polyethylenenaphthalate.
 29. A computer according to claim 26, wherein at least oneof the plurality of first insulating films and the plurality of thirdinsulating films comprises any one selected from the group consisting ofsilicon nitride, silicon oxynitride, aluminum oxide, aluminum nitride,aluminum oxynitride and aluminum silicide oxynitride.
 30. A computeraccording to claim 26, wherein the second insulating film and the fourthinsulating film comprises any one selected from the group consisting ofpolyimide, acryl, polyamide, polyimide amide, benzocyclobutene and anepoxy resin.
 31. A computer comprising: a display unit, the display unitcomprising: a first substrate; a second substrate; a light emittingelement and a thin film transistor, formed between the first substrateand the second substrate; a plurality of first insulating films formedbetween the first substrate, and the light emitting element and the thinfilm transistor; at least one second insulating film formed in eachspace between the plurality of first insulating films; a plurality ofthird insulating films formed between the second substrate, and thelight emitting element and the thin film transistor; and at least onefourth insulating film formed in each space between the plurality ofthird insulating films, wherein the first substrate and the secondsubstrate are formed of plastic, and wherein the at least one secondinsulating film has a smaller stress than that of each of the pluralityof first insulating films; and the at least one fourth insulating filmhas a smaller stress than that of each of the plurality of thirdinsulating films.
 32. A computer according to claim 31, wherein at leastone of the first substrate and the second substrate has flexibility. 33.A computer according to claim 31, wherein the plastic comprises any oneselected from the group consisting of polyether sulfone, polycarbonate,polyethylene terephthalate and polyethylene naphthalate.
 34. A computeraccording to claim 31, wherein at least one of the plurality of firstinsulating films and the plurality of third insulating films comprisesany one selected from the group consisting of silicon nitride, siliconoxynitride, aluminum oxide, aluminum nitride, aluminum oxynitride andaluminum silicide oxynitride.
 35. A computer according to claim 31,wherein at least one of the second insulating film and the fourthinsulating film comprises any one selected from the group consisting ofpolyimide, acryl, polyamide, polyimide amide, benzocyclobutene and anepoxy resin.
 36. A computer comprising: a display unit, the display unitcomprising: a substrate; a light emitting element; a plurality of firstinsulating films formed between the substrate and the light emittingelement; at least one second insulating film formed in each spacebetween the plurality of first insulating films; a plurality of thirdinsulating films; and at least one fourth insulating film formed in eachspace between the plurality of third insulating films, wherein the lightemitting element is formed between the plurality of third insulatingfilms and the substrate, wherein the substrate is formed of plastic, andwherein the at least one second insulating film has a smaller stressthan that of each of the plurality of first insulating films and the atleast one fourth insulating film has a smaller stress than that of eachof the plurality of third insulating films.
 37. A computer according toclaim 36, wherein the substrate has flexibility.
 38. A computeraccording to claim 36, wherein the plastic comprises any one selectedfrom the group consisting of polyether sulfone, polycarbonate,polyethylene terephthalate and polyethylene naphthalate.
 39. A computeraccording to claim 36, wherein at least one of the plurality of firstinsulating films and the plurality of third insulating films comprisesany one selected from the group consisting of silicon nitride, siliconoxynitride, aluminum oxide, aluminum nitride, aluminum oxynitride andaluminum silicide oxynitride.
 40. A computer according to claim 36,wherein at least one of the second insulating film and the fourthinsulating film comprises any one selected from the group consisting ofpolyimide, acryl, polyamide, polyimide amide, benzocyclobutene and anepoxy resin.
 41. A computer comprising: a display unit, the display unitcomprising: a substrate; a light emitting element and a thin filmtransistor; a plurality of first insulating films formed between thesubstrate, and the light emitting element and the thin film transistor;at least one second insulating film formed in each space between theplurality of first insulating films; a plurality of third insulatingfilms; and at least one fourth insulating film formed in each spacebetween the plurality of third insulating films, wherein the lightemitting element and the thin film transistor are formed between theplurality of third insulating films and the substrate, wherein thesubstrate is formed of plastic, and wherein the at least one secondinsulating film has a smaller stress than that of each of the pluralityof first insulating films and the at least one fourth insulating filmhas a smaller stress than that of each of the plurality of thirdinsulating films.
 42. A computer according to claim 41, wherein thesubstrate has flexibility.
 43. A computer according to claim 41, whereinthe plastic comprises any one selected from the group consisting ofpolyether sulfone, polycarbonate, polyethylene terephthalate andpolyethylene naphthalate.
 44. A computer according to claim 41, whereinat least one of the plurality of first insulating films and theplurality of third insulating films comprises any one selected from thegroup consisting of silicon nitride, silicon oxynitride, aluminum oxide,aluminum nitride, aluminum oxynitride and aluminum silicide oxynitride.45. A computer according to claim 41, wherein at least one of the secondinsulating film and the fourth insulating film comprises any oneselected from the group consisting of polyimide, acryl, polyamide,polyimide amide, benzocyclobutene and an epoxy resin.
 46. A computercomprising: a display unit, the display unit comprising: a firstsubstrate; a second substrate; a light emitting element formed betweenthe first substrate and the second substrate; a plurality of firstinsulating films formed between the first substrate and the lightemitting element; at least one second insulating film formed in eachspace between the plurality of first insulating films; a first bondinglayer formed between the first substrate and the plurality of firstinsulating films; a plurality of third insulating films formed betweenthe second substrate and the light emitting element; at least one fourthinsulating film formed in each space between the plurality of thirdinsulating films; and a second bonding layer formed between the secondsubstrate and the plurality of third insulating films, wherein the firstsubstrate and the second substrate are formed of plastic, and whereinthe at least one second insulating film has a smaller stress than thatof each of the plurality of first insulating films and the at least onefourth insulating film has a smaller stress than that of each of theplurality of third insulating films.
 47. A computer according to claim46, wherein at least one of the first substrate and the second substratehas flexibility.
 48. A computer according to claim 46; wherein theplastic comprises any one selected from the group consisting ofpolyether sulfone, polycarbonate, polyethylene terephthalate andpolyethylene naphthalate.
 49. A computer according to claim 46, whereinat least one of the plurality of first insulating films and theplurality of third insulating films comprises any one selected from thegroup consisting of silicon nitride, silicon oxynitride, aluminum oxide,aluminum nitride, aluminum oxynitride and aluminum silicide oxynitride.50. A computer according to claim 46, wherein at least one of the secondinsulating film and the fourth insulating film comprises any oneselected from the group consisting of polyimide, acryl, polyamide,polyimide amide, benzocyclobutene and an epoxy resin.
 51. A portableinformation terminal comprising: a display unit, the display unitcomprising: a first substrate; a second substrate; a light emittingelement formed between the first substrate and the second substrate; aplurality of first insulating films formed between the first substrateand the light emitting element; at least one second insulating filmformed in each space between the plurality of first insulating films; aplurality of third insulating films formed between the second substrateand the light emitting element; and at least one fourth insulating filmformed in each space between the plurality of third insulating films,wherein the first substrate and the second substrate are formed ofplastic, and wherein the at least one second insulating film has asmaller stress than that of each of the plurality of first insulatingfilms and the at least one fourth insulating film has a smaller stressthan that of each of the plurality of third insulating films.
 52. Aportable information terminal according to claim 51, wherein at leastone of the first substrate and the second substrate has flexibility. 53.A portable information terminal according to claim 51, wherein theplastic comprises any one selected from the group consisting ofpolyether sulfone, polycarbonate, polyethylene terephthalate andpolyethylene naphthalate.
 54. A portable information terminal accordingto claim 51, wherein at least one of the plurality of first insulatingfilms and the plurality of third insulating films comprises any oneselected from the group consisting of silicon nitride, siliconoxynitride, aluminum oxide, aluminum nitride, aluminum oxynitride andaluminum silicide oxynitride.
 55. A portable information terminalaccording to claim 51, wherein the second insulating film and the fourthinsulating film comprises any one selected from the group consisting ofpolyimide, acryl, polyamide, polyimide amide, benzocyclobutene and anepoxy resin.
 56. A portable information terminal comprising: a displayunit, the display unit comprising: a first substrate; a secondsubstrate; a light emitting element and a thin film transistor, formedbetween the first substrate and the second substrate; a plurality offirst insulating films formed between the first substrate, and the lightemitting element and the thin film transistor; at least one secondinsulating film formed in each space between the plurality of firstinsulating films; a plurality of third insulating films formed betweenthe second substrate, and the light emitting element and the thin filmtransistor; and at least one fourth insulating film formed in each spacebetween the plurality of third insulating films, wherein the firstsubstrate and the second substrate are formed of plastic, and whereinthe at least one second insulating film has a smaller stress than thatof each of the plurality of first insulating films; and the at least onefourth insulating film has a smaller stress than that of each of theplurality of third insulating films.
 57. A portable information terminalaccording to claim 56, wherein at least one of the first substrate andthe second substrate has flexibility.
 58. A portable informationterminal according to claim 56, wherein the plastic comprises any oneselected from the group consisting of polyether sulfone, polycarbonate,polyethylene terephthalate and polyethylene naphthalate.
 59. A portableinformation terminal according to claim 56, wherein at least one of theplurality of first insulating films and the plurality of thirdinsulating films comprises any one selected from the group consisting ofsilicon nitride, silicon oxynitride, aluminum oxide, aluminum nitride,aluminum oxynitride and aluminum silicide oxynitride.
 60. A portableinformation terminal according to claim 56, wherein at least one of thesecond insulating film and the fourth insulating film comprises any oneselected from the group consisting of polyimide, acryl, polyamide,polyimide amide, benzocyclobutene and an epoxy resin.
 61. A portableinformation terminal comprising: a display unit, the display unitcomprising: a substrate; a light emitting element; a plurality of firstinsulating films formed between the substrate and the light emittingelement; at least one second insulating film formed in each spacebetween the plurality of first insulating films; a plurality of thirdinsulating films; and at least one fourth insulating film formed in eachspace between the plurality of third insulating films, wherein the lightemitting element is formed between the plurality of third insulatingfilms and the substrate, wherein the substrate is formed of plastic, andwherein the at least one second insulating film has a smaller stressthan that of each of the plurality of first insulating films and the atleast one fourth insulating film has a smaller stress than that of eachof the plurality of third insulating films.
 62. A portable informationterminal according to claim 61, wherein the substrate has flexibility.63. A portable information terminal according to claim 61 wherein theplastic comprises any one selected from the group consisting ofpolyether sulfone, polycarbonate, polyethylene terephthalate andpolyethylene naphthalate.
 64. A portable information terminal accordingto claim 61, wherein at least one of the plurality of first insulatingfilms and the plurality of third insulating films comprises any oneselected from the group consisting of silicon nitride, siliconoxynitride, aluminum oxide, aluminum nitride, aluminum oxynitride andaluminum silicide oxynitride.
 65. A portable information terminalaccording to claim 61, wherein at least one of the second insulatingfilm and the fourth insulating film comprises any one selected from thegroup consisting of polyimide, acryl, polyamide, polyimide amide,benzocyclobutene and an epoxy resin.
 66. A portable information terminalcomprising: a display unit, the display unit comprising: a substrate; alight emitting element and a thin film transistor; a plurality of firstinsulating films formed between the substrate, and the light emittingelement and the thin film transistor; at least one second insulatingfilm formed in each space between the plurality of first insulatingfilms; a plurality of third insulating films; and at least one fourthinsulating film formed in each space between the plurality of thirdinsulating films, wherein the light emitting element and the thin filmtransistor are formed between the plurality of third insulating filmsand the substrate, wherein the substrate is formed of plastic, andwherein the at least one second insulating film has a smaller stressthan that of each of the plurality of first insulating films and the atleast one fourth insulating film has a smaller stress than that of eachof the plurality of third insulating films.
 67. A portable informationterminal according to claim 66, wherein the substrate has flexibility.68. A portable information terminal according to claim 66, wherein theplastic comprises any one selected from the group consisting ofpolyether sulfone, polycarbonate, polyethylene terephthalate andpolyethylene naphthalate.
 69. A portable information terminal accordingto claim 66, wherein at least one of the plurality of first insulatingfilms and the plurality of third insulating films comprises any oneselected from the group consisting of silicon nitride, siliconoxynitride, aluminum oxide, aluminum nitride, aluminum oxynitride andaluminum silicide oxynitride.
 70. A portable information terminalaccording to claim 66, wherein at least one of the second insulatingfilm and the fourth insulating film comprises any one selected from thegroup consisting of polyimide, acryl, polyamide, polyimide amide,benzocyclobutene and an epoxy resin.
 71. A portable information terminalcomprising: a display unit, the display unit comprising: a firstsubstrate; a second substrate; a light emitting element formed betweenthe first substrate and the second substrate; a plurality of firstinsulating films formed between the first substrate and the lightemitting element; at least one second insulating film formed in eachspace between the plurality of first insulating films; a first bondinglayer formed between the first substrate and the plurality of firstinsulating films; a plurality of third insulating films formed betweenthe second substrate and the light emitting element; at least one fourthinsulating film formed in each space between the plurality of thirdinsulating films; and a second bonding layer formed between the secondsubstrate and the plurality of third insulating films, wherein the firstsubstrate and the second substrate are formed of plastic, and whereinthe at least one second insulating film has a smaller stress than thatof each of the plurality of first insulating films and the at least onefourth insulating film has a smaller stress than that of each of theplurality of third insulating films.
 72. A portable information terminalaccording to claim 71, wherein at least one of the first substrate andthe second substrate has flexibility.
 73. A portable informationterminal according to claim 71, wherein the plastic comprises any oneselected from the group consisting of polyether sulfone, polycarbonate,polyethylene terephthalate and polyethylene naphthalate.
 74. A portableinformation terminal according to claim 71, wherein at least one of theplurality of first insulating films and the plurality of thirdinsulating films comprises any one selected from the group consisting ofsilicon nitride, silicon oxynitride, aluminum oxide, aluminum nitride,aluminum oxynitride and aluminum silicide oxynitride.
 75. A portableinformation terminal according to claim 71, wherein at least one of thesecond insulating film and the fourth insulating film comprises any oneselected from the group consisting of polyimide, acryl, polyamide,polyimide amide, benzocyclobutene and an epoxy resin.